Some bigger Wal-Mart's do allow you to stay one night... Usually as far out in the lot as you can get You'd have to check though...
Motorhome
You might get away with one night, however you may also wake up with a boot on your wheel. Walmart won't give you a warning, they just send a tow truck. Stay awake and alert cause most crimes happen in Walmart parking lots as well, good luck and God bless if you're struggling.
Mostly likely not
The official stance is probably no. No store would allow it. The question is whether or not the parking lot is patrolled by security or police. Good luck and stay safe!
Thanks! Your answer is awaiting moderation.