Boosted this season by an early, prolonged cold snap, Minnesota’s ice fishing scene continues to grow in step with the popularity of so-called “wheel houses,” tow-behind fish houses that increasingly resemble RVs.

“Business is booming for us,” said Chad Hiepler, office manager of Montevideo-based Ice Castle Fish Houses.

“We’ve been in it for 10 years and we’re still growing every year,” said Mike Draper, sales and marketing manager for Yetti Outdoors, maker of a competing, aluminum-framed fish house on wheels.

Both companies say demand has tilted toward bigger, more luxurious models that roll into state and national parks as travel trailers in the offseason.

Ice Castle’s double-axle, 30-foot-long “King’s Castle” sells for $43,500 and comes with two slide-out walls and an isolated bedroom. You need at least a three-quarter-ton vehicle to command the towing.

Yetti’s equally long “Grand Escape” features a cooking range, water heater, electric fireplace and wall space for a 43-inch TV.

Said Draper: “We are seeing a much bigger push into all-season use. But they all come with holes in the floor.”

Products from both companies now carry RV certification. Air conditioners for summer use have become ubiquitous. But ice fishing remains at the heart of the movement, and state fisheries managers keep tabs as wheel houses continue to bring new angling pressure to certain lakes.

“Is it a management problem? Not necessarily,” said Henry Drewes, northwest regional fisheries manager for the Department of Natural Resources (DNR) in Bemidji.

But Drewes said record angling pressure in recent years on Upper Red Lake, Lake of the Woods and Leech Lake has coincided with big increases in wheel house traffic. On Upper Red 10 years ago, he said, 75 percent of ice anglers were day visitors who fished an average of six hours per trip.

The wheel house revolution caused an inversion, Drewes said. Now 75 percent of hard water fishing on the lake is done by overnight visitors. The average duration has jumped to 48 hours. “It’s basically flipped in the past 10 years,” he said.

The “exponential growth” in rolling, hard-sided houses prompted the DNR to change fish house licensing rules. For years, wheel houses could avoid licensing fees under a loophole that only required licenses for “unoccupied” shelters — fish houses left on the ice for the season.

That changed Jan. 1 of this year and the DNR has increased its fish house and dark house license sales by 25 percent, year over year, according to agency data. As of a week ago, the DNR sold 50,253 fish house licenses in five categories for the 2017-18 season. Over the same period last season, DNR license sales in the five categories totaled 40,494.

Drewes said the missing income was needed by the DNR to keep up with added workload from wheel house anglers. For one thing, there’s more anglers to account for in fishing surveys conducted by DNR creel clerks.

In various circles around the state, Minnesota panfish anglers have raised concerns about added ice fishing pressures on crappies and bluegills. The advocates are critical of ice anglers who camp over winter holes of vulnerable, deep-water panfish. Too many fish raised from those depths die regardless of whether they are too small or too large to keep.

The trend — not unique to wheel house users — has figured into grass roots talk about lowering panfish limits in the state.

Drewes said the good thing about towable, hard-sided fish houses is that “more people appear to be fishing” on Minnesota’s frozen lakes, including families.

“It just seems like it’s not the grumpy old men on the lake experience,” Drewes said. “There’s lots of positives.”

Ice Castle is by far the market leader. Even as customers are trending toward more expensive models, overall unit sales continue to expand, Hiepler said. In 2016 when sales were increasing from the previous year, the Montevideo manufacturing plant was aiming to build 13 to 14 units a day. This year, with sales ignited by lots of good lake ice, production increased to 15 or 16 units a day.

“We’ve doubled in size in Montevideo over the past four years,” Hiepler said. “We’ve quadrupled in size over the past 10 years.”

Draper, of Yetti, said the market has been spurred by the availability of 15-year loans after lenders started to recognize the RV quality and craftsmanship that goes into the trailers.

“I have better cupboards in my Yetti than I do in my house,” said Brad Hawthorne, a pro fishing guide who lives on Mille Lacs.

Hawthorne said some ice fishing resorts were hostile to wheel houses when they first started to explode on the scene. Those resorts increased fees for trailers to access private ice fishing roads. Some resorts even banned the wheel houses altogether, he said. Those treatments are a thing of the past.

“It’s getting people fishing more,” Hawthorne said. “It’s only going to get bigger and bigger.”