base camp vs lean-to

base camp

noun
  • An encampment used temporarily for storing supplies and preparing for a larger activity, such as mountain climbing or hunting. 

lean-to

noun
  • A shelter with a sloped roof; also a building with a similar construction attached to the side of a building as an extension. 

How often have the words base camp and lean-to occurred in a corpus of books? (source: Google Ngram Viewer )