what is the shortest class c that people have used?

Didn't use it, wasn't even inside it: we were waiting for the ferry from Seattle to Victoria, B.C., and wound up behind a European Class C (Renault chassis? Can't recall), driven by a couple who had it shipped over from Europe to Halifax, Nova Scotia, and who had then driven it all the way across Canada and down into the U.S. They were preparing to drive it back across to Halifax before going home. It looked to me like the house portion was just about long enough for a bed and a little more room, but they were quite cheerful and clearly still having fun together.