In the past fifteen years, as underemployment becames more common and people see choices vanish, I've run into more than a few people who have been forced to live in minimalalist conditions.
° a mother and teenage daughter in a station wagon for over a year in Flordia
° a young woman trying to get on her feet in NYC renting renting a couch, bathroom priviledges and a half shelf in a refrigerator for $125 a month
° a young woman living in the San Diego area in a pickup for nearly a year
All very trying situations and fortunately these have been temporary situations, but I suspect they are increasingly common.
Some people have shifted to life in converted vans and (very) used RVs to save money, but others try to avoid fees associate with parking - a practice sometimes known as boondocking. Webpages with advice have cropped up. A few companies like WalMart see this as an opportunity (offer a place to park and get some business for nothing - even if it is modest, it is stil business), but it is generally discouraged. I'm guessing is is more common than we imagine.