Let's not forget Vacation, with Chevy Chase. So, it's not an RV, but you have to like the family truckster. ;D
Another movie with RV's is Into the Wild. It's not focused on RV's, but there's a lot of scenes with them, also a nice scene about slab city. Overall, a very good movie, imo.
http://www.imdb.com/title/tt0758758/