Here is a link to a NO Park Walmart site.
No Overnight Parking at Walmart – Walmart Atlas
We stay at Walmarts but check to see if they allow parking first. Normally Walmarts will allow parking unless there is a local ordinance not allowing it. A good hint is if you don't see other RV's.
You might also check for near by Sam's club, same as Walmart.
Cracker Barrel's allow parking but you need to ask to make sure and they usually don't want you parking really early.
We have stayed at most of the larger Trucks Stops without a problem although don't take a premium spot that easy for a truck to get into. Truck drivers need places to park and that's how they make their living. The last time we stayed at one we pulled off way to the side to make sure we left the better spots for the trucks.