When I was at the Tampa RV show in January, I purchased some products from a company called RV by Life. One of the products is called Graphix Wax and is designed specifically for vinyl graphics. It is a cleaner and UV protectant.
RV by Life is a division of Boat Life, a company that has been manufacturing products for boat owners for the past 50 years. They offer a full line of polishes and waxes. RV Wax | Graphix Wax | RV by LIFE
I haven't had a chance to apply any of the products I bought since spring weather seems reluctant to remain in Massachusetts for more than a few days a time.