shipping container houses could be made into houses or you could make your own from scratch and see what you might put inside.
There are folks who live in these and own trucks that carry them where ever they want set them down at a spot like a truck camper would and go off to the store or fish.
http://www.treehugger.com/files/2009/02 ... office.php
the below is a little big but on a small scale might be fun.
http://www.treehugger.com/files/2008/10 ... houses.php