The big key is the region the OP's son wants to van camp in. In Austin, it is possible if one isn't too obvious about it (vehicles have to be moved every 72 hours.) In most of California, just pulling over may get a visit from LEOs and a several hundred dollar fine.
There is also the size of the town. A small college town, a van may just be something that is OK, especially if a local place gives permission to park there, maybe even use water/electric. A bigger city usually has had so much crime that anything out of place will get investigated or have the police called on.