I 'express' travel a lot with my Class C, I routinely stop in rest areas (all over North America) and have found, and been told by LEO and officials both, that these overnight parking laws are merely a tool.
It allows them to tell someone to move along with the authority of law. It does not mot mean it's enforced.
On my last trip a had stopped for the night in a rest area and was walking Deputy Dog before turning in, a police officer parked there guessed by my parking at the far end I was overnighting. As I passed near he put the window down and asked. When I said "yes" his only reply was to move to a certain place directly under a light instead. He said that put us directly in their line of sight and 'they could keep an eye on us more easily".