I think a trailer that your family could live in for awhile is a great idea. That purpose was not what I was setting out for when I got my teardrop trailer, my purpose was camping, but I'm mindful of its utility in a crisis.

Mine is kept in storage well outside the city, near the mountains where we frequently camp (and upwind of DC). It's permanently packed with everything except food and water. Clothes, jackets, gloves, hats, etc. are in the teardrop all year.

R-11 insulation makes it toasty with no heater into the 30s. Zero-degree sleeping bags are key if it dips below that.

Here's a terrific resource if you're interested in building a teardrop or small "standie" trailer, buying, or converting a cargo trailer to your needs.

A lot of folks have solar setups. You can find a lot of info on that at this link, as well.

http://www.mikenchell.com/forums/index.php

Here's the cargo trailer conversion section of the forum:

http://www.mikenchell.com/forums/viewforum.php?f=42&sid=84767606bb2c3022b9533f4a60c6b0d0