I started with a cargo ('box') trailer from Pace; it's pretty good. Then I started building in walls and goodies. The computer talks through the speakers of the radio; it lets me know when it's time to wake up, warns me of things, etc.
I have a QUEEN sized bed, a shower/potty that's 3ft-by-4.5ft, central heat, A/C on the way, and comfy storage room. I also have a full-sized computer workstation and did it in only 14 feet. When you break all the "RV Rules" you can do whatever you want!
The plan is, when Mom no longer needs me, to take the vehicle out on the road and tour the 46 states I visited before I was 15. Then do the rest.
If you're interested, here are some photos. Keep in mind it's still under construction. I hope to give people ideas.
Photo Gallery: The CounterMoon