MONTEVIDEO— Across Minnesota 7 from the Walmart, American Surplus offers an eclectic array of wares: cheap sunglasses, popcorn, refrigerator magnets.

You’d never know it from the selection in the aisles, but this is the epicenter of a revolution in ice-fishing houses.

In the back of the warehouse-like building, about 80 workers furiously are building Ice Castle ice-fishing houses, the brand that is rapidly becoming ubiquitous across the Upper Midwest’s ice-fishing belt.

As the ice thickens and holiday tasks are laid to rest, perhaps as many as 11,000 Ice Castles will be towed across frozen lakes, where they’ll join the ranks of generations of home-fashioned ice houses that form the shantytown communities that annually spring up above sand bars where walleye, perch and other fish will, with any luck, be hooked all winter long.

When you think of a wheelhouse that can be hauled along the highway and onto the ice road and then lowered onto the ice, you probably picture an Ice Castle.

In one of the worst economies in generations, the brand continues to grow, to the point where “ice castle” is becoming a generic term for wheeled ice-fishing houses. The company is scrambling to keep up with orders, and a slew of competitors — including national recreational-vehicle makers — are entering the fray.

The brand claims 56 percent of the market share in Minnesota; in January, 178 units were sold, compared to 19 by its nearest competitor. According to Omaha, Neb.-based A.C. Nelsen RV World, the top-selling travel trailer recreational vehicle (ice house or not) in Minnesota is the Ice Castle. Eat your heart out, Winnebago.

“We didn’t know it was going to be this big,” confessed Jeff Drexler, the owner of American Surplus, which owns and builds Ice Castles in Montevideo, with almost exclusively American-made parts, many manufactured in Minnesota. “It’s huge.”

It all started on a whim.

In 1997, Drexler, a 61-year-old native of Stratford, Wis., who ice-fishes only occasionally, got a call from friend Dave Hanlon, store manager at Milaca Unclaimed Freight, a landmark on U.S. 169 for Twin Cities anglers driving to Lake Mille Lacs.

“We used to make storage sheds, and one of the employees at Milaca Unclaimed Freight said, ‘Why don’t those guys make an ice-fishing house trailer,”’ Drexler recalled as he sat at his paper-strewn desk. “No one else was really making houses like that, and so I said ‘Sure, let’s make one.’

“Pretty soon, every one we made was being sold, and people wanted more.”

The first models were nameless, 6.5-by-12-foot boxes priced at $1,999. The company now offers 33 models, with a new one to be unveiled at the Minneapolis/St. Paul RV, Vacation & Camping Show on Feb. 6-9 at the Minneapolis Convention Center.

American Surplus’ top-end model is the luxurious King’s Castle, which stretches 8 by 30 feet (with a V-shaped front for extra space) and has a suggested retail price of $36,250. The smallest, most spartan model — the Scout — sells for just under $5,000.

You’d think that the economy that put a sleeper hold on sales of motorboats, snowmobiles and other (supposedly) nonessential purchases would have hurt sales of $30,000 ice houses.

Not so.

“The economy never slowed us down,” said Drexler, whose two grown sons work at the plant. “We’ve had no layoffs and have expanded a number of times. We started with five employees, and now we have 102.”

How can this be? In a word, versatility.

Ice Castle doesn’t own patents on any key components or designs, but it did show the world how versatile its products can be.

Five years ago, Drexler set up one of his Ice Castles at the Minnesota State Fair with an air conditioner inside.

“Everyone thought we were nuts,” he said. “Why would you put an air conditioner in an ice house?”

“These aren’t just ice-fishing houses,” said Bob Fielder, general manager of A.C. Nelsen RV World, which has a retail outlet in Shakopee. “They’re RVs you can fish out of in the winter and camp with in the summer; some have party decks. They can be hunting sheds and toy haulers, too.”

One common innovation in many Ice Castles — and some RVs, in general — is a feature in which the back end opens into a ramp. ATVs, snowmobiles, dirt bikes and the like can be driven right into the “living room,” which is fitted with tie-down anchors.

“This is huge because, in Minnesota and Wisconsin, camping is so big the rest of the year,” Fielder said as he showed off a list of features at a recent ice fishing expo: LED lighting, solar-charged battery power and wiring for a catalog’s worth of electronics, including depth finders and underwater video cameras.

Being an RV — officially — has other benefits. Some campgrounds won’t accept “ice houses on wheels” for safety reasons, and banks are reluctant to finance the purchase of such a contraption.

That’s why, several years ago, Drexler obtained official certification from the Recreational Vehicle Industry Association for larger Ice Castle models. (Fielder tells customers that, if an RV has plumbing, it might qualify as a summer home, which might allow interest to be tax-deductible.)

“It legitimized what we were doing,” said Karen Bogan, who leads sales and marketing for Ice Castle. “It made it a lot easier to explain to people that, yes, this really is an RV, and it meant you could finance them from your local credit union.”

Bottom line: There’s more demand for Ice Castles than there are Ice Castles.

“We can never get enough,” Fielder said. “They all sell. That’s one reason in the last year you’ve seen some of these other competitors coming into the market.”

Inside the various buildings in Montevideo where Ice Castles are made, workers saw, spray, drill and pound away at an impressive pace. Aside from the trailer base, only raw materials arrive here. With few exceptions, most of an Ice Castle is assembled from the trailer bed up, including a corner where woodworkers build cabinets.

And this isn’t robotic assembly; electricians snaking wires lean over carpenters roughing in doors. Supervisors with clipboards, often with hand-scribbled drawings and notes for custom modifications, attempt to choreograph the work.

“Last year, we produced 1,422 ice houses, and this year we’ll do 2,040,” Drexler said. “These guys are working six days a week, and we’re up to 10 units a day.

“And we’re about 500 behind.”