Check out
http://www.allstays.com They have lots of information including some very detailed spreadsheets (also books) on campgounds and other faccilities some of which, like Walmart, Lowes, Cracker Barrel, Pilot-FlyingJ that allow free overnights (not camping, just park for the night).
I've found the owner is very active keeping the data up to date.
I have all the pertinent Excel spreadsheets on the RV support computer.
Regards,
Jim