I don't know as it is any better than this:
http://www.tinyhousedesign.com/2009/06/08/snail-shell-system-tiny-rolling-shelter/ Both of them are better than sleeping in a doorway, but both are on the street in a very public way. While most of the snail is not expensive.... the polly container itself is going to want to be new, I think, as anything I can think it may have been used as in a former life is not something that would make me want to use a used one to live in
On the up side, it is easy to move... though probably not as easy as a shopping cart or (in our area) a bike with a trailer, that most of the homeless use. Those who are "the working homeless", pretty much always have a car or van and the interior volume is as much as either one of these two ideas and less in your face as well.
When I was doing this, I used a 1/2 ton van, I used black garbage bags on the windows so it was not obvious that there was someone sleeping inside. I parked close to the marina where they have a public bathroom open till 10pm and there are showers at work. As it was my daily ride, it was never parked anywhere long
enough to bring trouble.... and it was lockable. Cost? Van-$1000, insurance and licensing - $1000/per year and gas varies, but all of these costs were costs I would have had anyway just to get around. Why? it was just before we moved here and my family was living in another
city with a
mortgage I had to pay while we waited for the house to
sell.