What are the challenges frightful Sam and mole face in frightful mountain in chapter 15

In chapter 15 from the "Frightful mountain" is said that September cames with fall. So, naturally, the animals start to hybernate. It’s 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.