We've had numerous discussions here about "camping at WalMart", some of them turning negative. For whatever reason, folks think that WalMart's security is there to protect them (the campers/overnighters). Folks also try to convince us that they're really not trying to save the cost of a campsite, because they "spend $30 at the store". Hm, if we need $30 of goods at WM, we don't assume we could/should stay overnight at a WM parking lot.
Even in daylight hours, I've seen too many drug activities in the corner of a WM lot. Add that to the fact that a WM store would likely be in the low rent district of a town we don't know, and we'd move on to the next campground.
Apologies if my recollection is a little vague ... some years ago it was reported/linked here that a family travelling across country (en route to Disneyland) in an expensive motorhome, stopped for the night at a WM. Late in the evening there was a knock on the door and the owner was confronted with a druggie. When the druggie tried to acost the guy's daughter, he opened fire killing the guy. No charges were brought, but the family was stuck at the site for a week while police investigated. I doubt they enjoyed their vacation, or are likely to use that RV again.