Check out Rejex. You have to remove all of the old wax before applying but if you do it by their instructions one application will last several months if not a year depending on where you live and how you store your RV.
Our RV is stored outside and we apply Rejex in the spring and fall. We also apply a fresh coat to the front before each trip and most of the bugs will wash off with just a garden hose. We also apply it to the windshield and in my opinion it works better than RainX.
RejeX: Nothing Sticks but the Shine!