MINNEAPOLIS — Seventeen-year-old Rudy Hummel hasn't let one of the coldest winters in decades, drenching rain or clouds of mosquitoes prevent him from sleeping outside every night for a full year.

Hummel was preparing Friday to spend one last night in his treehouse at his family's home in Hermantown, near Duluth, making it 365 straight nights outside. He endured 76 subzero nights in a snow cave. The Boy Scout would pitch a tent while traveling, even using a hotel's deck. By his count, he slept outdoors in 30 different places.

Hummel's experiment became a fundraiser along the way for Habitat for Humanity and the Hawk Ridge Bird Observatory in Duluth. He invited friends over to sleep in his yard for his last night and urged other people following his adventure to donate and join them by sleeping out wherever they are.

Winter nights weren't so bad, Hummel said, even when it got down to 27 degrees below zero one night. His cave, a hollowed out pile of snow called a quinzhee, kept the temperature about 10 degrees warmer than outside. But mostly he relied on layers — a fleece liner inside a mummy bag inside two other sleeping bags, with two or three quilts over that. He'd wear up to three layers of pants and up to seven shirts.

"The worst nights of all were actually during summer, the really hot, humid nights" that often turned stormy, he recalled. "I would be completely drenched with my own sweat."

Two nights were especially tough, Hummel said. One was last summer, at Woodland Caribou Provincial Park in Ontario, when he used a hammock with a mosquito net.

"There were so many mosquitoes that I couldn't get to sleep because the buzzing was so loud," he said.

And there was a rainy night as the snow melted this spring. He decided his quinzhee was unsafe so he pitched a tent on the driveway and got soaked moving his gear.

"That's the only night where I've actually been cold," he said.

Hummel said he got the idea last April to spend every summer night in his treehouse. In August, he decided to go for a full year. In December, he turned it into a fundraiser and started a website with links to his two charities. He chose Habitat because he could have gone inside anytime, but knew that some people don't have that choice. He also picked Hawk Ridge because he learned that the squirrels, owls and other creatures sharing his backyard weren't just visitors. He had raised about $4,000 as of Thursday.

Hummel had mixed thoughts about the end of his experiment, mainly because his bedroom was in "dreadful" shape after a year of disuse.

"I will have to do a significant amount of cleaning before I can lay in my bed," he said. "It's amazing how much stuff accumulates in a place you don't use."

His parents are proud, but his mother, Gail Johnejack, laughed at the suggestion that she might be happy to have him back safe inside.

"If he pulled this off I'm pretty confident he could pull whatever off," she said.