We have overnighted at rest stops in Ohio. And rest stops in NY, along with more than 20 other states. We have never been bothered by cops, criminals, transients (aren't we transient in many respects?), or truckers.
Sometimes, Flying J/Pilot and other truck stops will have an RV parking area. We use those too, but will not park in the truck area - we aren't a truck and they need those spaces.
We tend to avoid Walmart unless we are really desperate. In small towns, it often seems to be the only place for teens to gather and hang out.