Do they allow overnight parking?

Not sure what kind of vehicle you're wanting to park overnight, but the parking lot isn't set up anything big to stay. I'd call the manager, but it's not customary. Usually the truck stops off the interstate are much more well suited, and you'll have access to a clean restroom. Wal-Mart's allow overnights, but I'd check with the manager before parking anywhere that isn't open 24 hours.

Walmart let's you stay there

If you ask the management, they sometimes allow it.. otherwise it could be towed at owners expense...