National RV in Detroit says "It can be argued that parking on concrete can cause flat spots on your RV tires, but overall we feel that a full pad of concrete would provide a durable and ideal parking surface. Concrete doesn’t contain petroleum-based products like the ones used in asphalt, so you don’t have to worry about chemicals clashing and causing damage. As far as water drainage goes, we would highly recommend shaping your concrete pad so that it is crowned and water can drain off rather than collect around your tires."