First of all, I don't agree with Jamie; staying in nice neighborhoods will not work. People don't like looking out their windows and seeing mysterious vans parked across the street, especially when all the other cars are Audis and Mercs and shit.
Is the USA really divided into GHETTO and PLACE WHERE PEOPLE DRIVES AUDIS?
I live in Canada in a pretty nice part of town (it's not full of rich people but crime is extremely low) and a van would fit right in, so long as it wasn't a complete pile of poop. Doesn't the place where you live have middle class neighbourhoods? I think living in a van in Canada (at least my part of it) would be a lot easier, mostly because vans aren't constantly being broken in to and their occupants slain while asleep. I can think of, like, fifty locations I could park a van overnight both be totally inconspicuous and take a snooze and feel totally safe within twenty kilometers of where I live now. This would be even easier if you got a solid-paneled van instead of something with windows since no one 'round here comes up and peers in to the cab looking for sleeping dudes.
Also, if you parked in a parking lot you could just use the corners/sides nearest to the building. I see cars in parking lots for no feasible reason all the time. You could park in transit parking lots, since lots of people leave cars there overnight.
Why is crime in the US and the UK so high? Cripes guys! It's scary to think you can't even sleep in a van with locked doors and not get robbed!
p.s. I live in the biggest city in Canada so it's not like I live in a quaint small town where crime is nonexistent!
edit: living in a van is a pretty bad idea unless, like, your mom let you use her bathroom every morning to wash up and whatever. Even still it's a pretty horrible idea, although driving to work IN YOUR HOUSE would be pretty cool!