I was thinking of something like an enclosed lifeboat/semisubmersible. Definitely not a sailboat, although I suppose you could step the mast.
It's been a while since I posted this. It was added to an album in 2014:
It was designed as an ice fishing hut for an architecture class in college, but would work as an outhouse. I think the drawback as an ice fishing hut is that slush kicked up on the underside would freeze the door shut.