My favorite "living in a van" story is http://www.hobostripper.com/

(I wonder how much worse a van is than a military trailer. Those range from 40x12 with private bathroom and nice furnishings down to 10x8 with a roommate and no bathroom. It's probably a lot easier due to everyone else around you doing exactly the same thing, and there being portapotties, shower trailers, etc. freely available.)

I lived in a car for a month or so around the Bay Area (mostly because it was easier than finding an apartment); I'd do a hotel once or twice a week (and stay from 6am one day to 4pm the next day), and a 24h fitness membership (showers, etc. nationally) is $10-12.50/mo through Costco. I really wouldn't recommend car living, though.