The following link is to a group that is moderated on Yahoo that keeps tabs on the WalMarts (US only) that allow overnight parking. They spell out what is the accepted behavior, they have lists of the ones that do NOT allow overnight parking and they also seek to promote better relations between RVers and WalMart. There are a bunch of other type stores that also may allow overnight parking to perhaps a lesser extent, some of these are Sam’s Clubs, Flying J and KMart, among others.
I thought that someone could use the info that could be gleaned from joining this group. I know Tiny Housers may not be that big on WalMart, but if you are traveling with your house and have nowhere to go, it could help.