Lenny Cooper is a top seller in the hick-hop genre.

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From Georgia to Texas this weekend, the stars of a budding musical genre known as "hick-hop" will perform in swamp-like off-road-vehicle parks. Singing songs that fuse hip-hop with country music, the bands will celebrate the popular rural pastime of driving trucks, lawn mowers, golf carts and even jacked-up grocery carts—all through the mud.

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The music, anathema to country-music traditionalists because of its heavy drum and bass, doesn't get much airplay on major radio stations. But the all-ages mud-park shows, which feature dancers that shimmy around chain-link-fence poles cemented onto truck beds, can draw upward of 10,000 fans. They tend to spend freely on CDs and merchandise, from moonshine to Mason jars filled with the mud used in a band's music videos.

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Three of the genre's top artists—Colt Ford, Lenny Cooper and the LACS (short for the Loud Ass Crackers)—have albums among the top 75 on Billboard's country music chart this week with 1,800 Wal-Mart stores around the country stocking their records. Average Joe's Entertainment, a Nashville, Tenn.-based independent record label that specializes in the emerging genre, has sold nearly 200,000 "Mud Digger" compilation albums featuring its various artists; the fourth "Mud Digger" album hit stores Tuesday.

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The unlikely rise of this niche genre, despite its near-absence from radio, shows how radically the music industry's playbook for success has changed in recent years. Record sales have tanked nearly 60% since their peak in 2000, with the proliferation of outlets offering music free or at a nominal cost. So live performance and merchandise sales represent an increasingly large chunk of a typical band's income.

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To maximize concert revenue, hick-hop artists are using some of the same technologies that have eroded record sales to ferret out paying fans. They're routing tours based on data from services like Songkick, TuneCore and Pandora that track where people are buying or listening to their music most frequently.

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Big retailers like Wal-Mart have also become a way for artists to reach millions of listeners without radio or record-label deals. Wal-Mart, which accounts for about 10% of total music sales in the U.S., according to the market researcher NPD Group, has taken to buying music directly from musicians in recent years, selling millions of albums even as industrywide sales decline.

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The increase in bands circumventing traditional channels has given rise to a number of quirky musical styles. Though hick-hop has been more commercially successful than most, Internet radio service Pandora counts 400 genres popular among its 70 million active users, from psychobilly—a fusion of rockabilly and punk—to trap, a hip-hop-influenced subset of electronic music.

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Mud bogging has been a popular activity for decades, especially in the South, but the mud world's musical tradition is recent, with live-music stages sprouting up in at least 162 off-road-vehicle parks over the past five years. Fans typically pay about $40 a weekend to cook out with friends and play in the mud with a wide range of vehicles, from $100,000 trucks to homemade contraptions fashioned from tanks, lawn mowers, even king-size mattresses, all jacked up on giant tires forbidden on city streets.

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The scantily dressed crowd includes grade-schoolers, teenagers driving their parents' farm equipment and professionals who burn thousands of dollars each week on truck repairs, only to demolish their rides again the next weekend in events like truck tug of war. Daisy Duke shorts, bikinis and anything camouflage are popular fashion choices; homemade moonshine and beer are on tap and truck brands tend to be American, as Colt Ford notes in his "Drivin' Around Song": "U.S.A., Chevrolet, Dodge and Ford, raising a little hell and praising the Lord."

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The underground world even has its own magazines: Mud Life sells about 70,000 copies a year, thanks in part to its "Mud Girl of the Month" feature. The community's official afterparty is known as Club Mud, started by two friends who constructed a makeshift stage with speakers and lighting on a yard cart made for hauling hay. Now the pair throws weekly parties for up to 8,000 people from Missouri to Michigan.

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The culture's unofficial soundtrack was born during the summer of 2008 after Colt Ford—a former pro golfer with a devoted Myspace following—decided to launch the record label Average Joe's with veteran hip-hop producer Shannon Houchins. The music featured catchy country hooks and traditional country instruments like fiddles and washboards, but Mr. Ford spoke the lyrics instead of singing them, focusing on rural themes like hunting, fishing and driving big trucks through mud. After releasing Mr. Ford's debut album on iTunes, Mr. Houchins got a call from the owner of an off-road vehicle park in South Carolina offering Mr. Ford $3,500 to play a show there. About 4,700 fans turned out, snapping up $10,000 worth of merchandise, as many fans had gotten so wet and muddy that they were happy to buy a fresh change of clothes.

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Mr. Houchins, who helped artists like Bubba Sparxxx mix country and hip-hop in the past but had never before tried to hawk the final product, said he realized he'd found an untapped market. He began reaching out to scores of other off-road-vehicle parks. Since most weren't equipped to host concerts, he connected them to ticket printers, security staff and stage builders. The parks booked a string of mud-bog dates for Mr. Ford, and the LACS played as an opening act.

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Thousands of fans jammed onto rural two-lane roads to see Mr. Ford and the LACS rap about the mud lifestyle, and they soon began seeking CDs in local stores. Mr. Ford's "No Trash in My Trailer" has lines like: "I'm mud boggin, camouflagen, a ballgame is what I'm watchen. I work hard, mow the yard, fish, hunt, knuckle scar, change oil, plow the soil, love a boat country boy." Mr. Ford has sold more than one million albums to date.

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That year, Wal-Mart started getting calls from stores across the Southeast from customers complaining that mud-themed music was only available online, said Tiffany Couch, sales director of Select-O-Hits, a division of closely held Anderson Merchandisers that Wal-Mart hires to supply its 4,000 Supercenter stores with CDs. Cautiously, she said, they began stocking several hundred Wal-Mart stores in the region with the music, waiting to make sure it sold before expanding to other locations.

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Wal-Mart has long been supportive of little-known community artists—especially in the country-music world, Ms. Couch said. The company sponsored a free concert series in its store parking lots in 1995, for example, that featured up-and-coming country acts such as the Smokin' Armadillos and the Moffats. But hick-hop's quick success came as a surprise. "It's atypical in country music to have achieved this level of success without radio being the main driver—this has been kind of an enigma," said Ms. Couch.

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To be sure, Wal-Mart's power in the music industry is fast diminishing as demand for physical CDs shrinks. But country fans have been far more reluctant than others to go digital. Big-box retailers account for about 50% of country-music sales, compared with 25% of music sales in all genres, according to Nielsen Entertainment analyst Dave Bakula.

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Wal-Mart has made a string of exclusive deals in recent years to release new works by aging superstars like the Eagles and Journey. For budding acts, the stores present a valuable opportunity to connect with millions of potential fans on a national scale.

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Jason Lathrop, an air-conditioning contractor in Jacksonville, Fla., said he bought every album in Average Joe's catalog he could find because he spends most of his free time driving his souped-up Ford Excursion "out in the middle of a cow pasture somewhere," where the music has fast became ubiquitous.

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To assure Wal-Mart about its prospects for selling more mud music outside the Southeast, Average Joe's last year showed the retailer "heat maps" drawn up by Pandora. The maps showed where Pandora users were listening to the new genre most frequently, landing the records in nearly half of Wal-Mart's Supercenters nationwide. Average Joe's also began using Pandora's heat maps to route artists' tours through unlikely areas with high fan concentrations, like Ohio, Indiana and the Pacific Northwest.

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Pandora founder Tim Westergren said he started a pilot program over the past year and half which shares these maps with about 50 different groups. The company has finally amassed enough listeners so that bands can convert the data into significant concert ticket sales. More than 10,000 of the artists Pandora plays have now been listened to at least 250,000 times each, he said.

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"It's the folks that can really make the live thing work that are going to thrive," said Mr. Westergren, adding that Average Joe's "has been way out in front in terms of understanding how valuable" the maps can be.

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The LACS have now sold nearly 200,000 albums and an additional 25,000 singles on Apple's iTunes store, despite hardly any play on radio. They will release their third album in August, as they quadruple their touring business.

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Country rap dates back to at least the late '90s, and before that country legends like Johnny Cash used recitation instead of singing on some of their most popular tracks. But in the past, country rappers have struggled to sell records for lack of a defined audience. Though the two genres share the same roots and many of the same general themes—drinking, driving around and having a good time—their fusion has been controversial, says Adam Gussow, a Southern Studies professor at the University of Mississippi.

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"Country and rap have achieved much of their contemporary popularity by configuring themselves in the national imagination as proudly radicalized genres: the voice of the unreconstructed Southern pastoral and the rural white-working class on the one hand, and the voice of inner-city frustration, gunplay and rump-shaking Vegas-style fantasy on the other," Mr. Gussow wrote in a 2010 essay in Southern Cultures journal.

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But the new hick-hoppers have targeted a specific audience, taking more care than their predecessors to keep their language relatively family-friendly and the themes lighthearted and violence-free.

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"We never killed nobody, so we can't rap about no gangster stuff," Mr. Sharpe told a half-baffled, half-riveted crowd at the Country Music Association's flagship music festival in Nashville last month, as the band used synthesizers and 808 drum machines to accompany their hit tunes like "Kickin' Up Mud." Lyrics reflected their lifestyle: "Everyday get stuck in a big mud hole/Just sit right there and watch the sun get low."

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Hick-hop artists say the mud world is endlessly inspiring. Lenny Cooper, an artist better known as the "Mud Digger King," said that after he noticed scores of fans in Florida and Georgia installing homemade stripper poles in the back of their trucks, he wrote a song called "Rodeo," an ode to truck-bed strippers. He also wrote a song about a technique many of his mud-crazy fans used to center themselves: "Just somethin bout chillin out where the corn grows/I like to clear my mind down an old back road."

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Mr. Houchins, of Average Joe's, said he has been receiving about 500 demo tapes a week from country rappers lately. "That tells me that we're creating a new genre," said Mr. Houchins. "But they haven't made a Grammy category for us yet."