No, the stories aren't plausible. They aren't meant to be. He's writing in the tradition of Robinson Crusoe, but for young readers. The point is the adventure, self-reliance, and the reinvention of lost technologies (fish traps, making a bow and arrows, etc.) Paulsen was a hunter as a kid. You might also enjoy his non-fiction, autobiographical (he says) book "Guts." He also published a book about his youthful adventures. I'll find it and send along the title. Personally, I like his books, but I find the older books more satisfying, and I think I like Jean Craighead George's books better. Read the Julie trilogy. The main character is an Inuit girl, but I think you guys can handle that.
Richard