Any big wide open parking lot works for us when needed. Rest stops. Truck stops of course. Even stop into those 24 hr gas station places if they have that bigger parking lot and pull thru behind in some locations to get out easy after parking and ask to just park and sleep. They always say fine!
In late, out very early. If we can ask we will, if all is closed we just go off and park and get those few hrs of sleep and fire up quick and hit the road again. HD would be a defininte place we would stop if needed.
Never had troubles of any kind. If it looks fine for a fast sleep stop we would try it :)