Wat is one challenge frightful faced in chapter 15

In chapter 15 from the "Frightful Mountain" is said that September cames with fall. So, naturally, the animals start to hibernate. It means that Sam will face with that problems as exposure. Sam decided that if he wanted to keep warm, he would have to put clay to cover his tree. He also decided that he needed a fireplace. But, as he tried to make a fireplace for days, he realized that it would not work.