Douglas C. Pizac, Associated Press
Russ and Celeste Faust of Denver walk their dogs past recreational vehicles in Yellowstone National Park, Wyo., in June.

YELLOWSTONE NATIONAL PARK, Wyo. — In the heart of the park here on a recent warm day, all 358 spaces at the Fishing Bridge Recreational Vehicle Park were jammed with RVs and camping equipment.

Despite high fuel prices and a sputtering economy that have hurt RV sales and caused many people to put the brakes on vacation plans, plenty of the lumbering, gas-guzzling rigs have taken to the road this summer.

"If you want to stay out here and do this, you just suck it up and go," said Leyman Williams, lounging on a folding chair outside his 39-foot RV at Fishing Bridge

The Williams live year-round in their motor home, which has all the comforts of a traditional home — running water, refrigerator, kitchen, private bathroom and bed space for up to six people.

But the huge vehicle gets only about 10.5 miles to the gallon. With diesel prices above $4 a gallon much of the summer, filling the 90-gallon tank means shelling out around $400.

"I learned to drive a little slower," William said, noting the RV gets better highway mileage at around 60 mph.

More than 1.1 million RVs visited National Park Service campgrounds through the first seven months of this year, according to preliminary figures.

The numbers are down about 6 percent from the same period last year, said Park Service spokesman Jeffrey Olson. But July and August are the busiest months for RV camping in national parks and many campers are out during the fall, he said.

RV and campground trade associations say 2008 appears to be just as busy as previous years, though with some variations that could be attributed to fuel prices.

A survey earlier this year by the Virginia-based Recreation Vehicle Industry Association found that high fuel prices weren't stopping RV travelers, but in some cases were prompting shorter trips, said Kevin Broom, spokesman for the 550-member association.

Perhaps more importantly, the association expects a 14-percent decline in this year's RV sales. That comes on top of a 9.5-percent drop last year.

Broom said the same economic forces plaguing the housing market affect RV sales. Manufacturers have responded with new designs over the last several years to emphasize fuel efficiency. The large, luxurious RVs get as few as 6 miles to the gallon, while the smaller ones can get up to 18, he said.

While fewer people are buying RVs, more are renting them, Broom said. On average, RV rentals cost about $1,500 a week, he said.

Even with the higher fuel prices, Broom maintains RVs are still an economical way to vacation because RV users save money on the motel and restaurant bills that are part of traveling by airline or car.

"The savings overwhelm any fuel cost increases, especially when you can adjust by instead of, say, taking a 1,000-mile trip, you take a 100-mile trip," Broom said.

Some RV enthusiasts compromise on their vacations by parking their RVs for the summer at a close-to-home campground and staying there on weekends, said Linda Profaizer, president of the National Association of RV Parks and Campgrounds.

"People are somehow adjusting their lives, not that it's not a hardship for a lot of people to have to pay more for gas and everything," she said. "But it's still important for them to get away and enjoy themselves."

For the Williams, that means driving their RV a little slower, bypassing engine-straining mountains and staying longer at the places they visit. They also tow along their small sport utility vehicle, which gets close to 30 miles to the gallon, and use it to get around the area they are staying.

Williams said any mileage lost in towing the vehicle is exceeded by the savings from not having to drive the RV short distances to the grocery store or to see area attractions.