Exactly! Most RVs are much smaller, and lots of retired couple live in them. The big problem is that in many, many, parts of the country the Zoning police would evict you because it is not allowed by their law.
There are a lot of advantages to living in a small space. Most people would be better off with a smaller house and a bigger 401K.
For a while I lived in a full size, full feature, over the cab camper on the back of a pickup, people thought it was small living quarters and if course it was for a house, but like I told them, it is an utterly fantastic bedroom.