I actually contacted the corporate headquarters of 15 stores to get confirmation. You can see the results here: https://camperfaqs.com/what-stores-allow-overnight-rv-parking
Walmart, Cabela’s/Bass Pro Shops, Sam’s Club, and Love’s are just a few that I can confirm allow overnight parking on a store-by-store basis. Of course, always call ahead and confirm that overnight parking is allowed at that particular store.