I built my own trailer, a "tiny home": http://tinyhousemansion.com/

I filmed a several how-to videos and put them up on youtube. Not the most economical (cost/resale-wise), but a great experiment and real-world break from full-time programing.

My Tiny House is super insulated and energy efficient. The only leaks are from windows. I wrapped the whole thing in rigid foam panels and lifted the metal roof up an inch to keep the roof from ever getting hotter than the ambient air temperature.