Sams Club parking

I napped in Walmart, Cracker Barrel, Costo and Menards parking lots. Never 'camped' in any though.

Similar to Walmart, the decision is up to local manager -- or subject to the city regulations.

it's best to ask the manager of each particular location, or call ahead before arrival. Good manners would also dictate purchasing something from the location before you leave, even if it's just a snack or something inexpensive