I use Aero Glaze. It's a combination dry wash/wax that is intended for aircraft, but works extremely well on my RoadTrek. It's not cheap, but it can't be beat for ease of use and the wax holds up extremely well. As long as the RV isn't too heavily soiled, you can use it per the instructions to clean as well as wax, but I have always at least hosed off the vehicle first if there is an accumulation of dirt and grit on the paint. Aero Glaze is available online from sources such as Aircraft Spruce or Sporty's.
There's also another aircraft-related product called simply "Helicopter Polish" that is made for cleaning the bubble canopy but works well on anything plastic. As the name implies, it is strictly a polish that leaves behind a protective film, so you will need to clean first using some other product.
I especially like Helicopter Polish because it doesn't leave behind any sort of build-up like Turtle Wax. I used to use Turtle Wax all the time, but was always disappointed to find dried, white wax in crevices and along edges several days after I thought I had thoroughly buffed it out. Helicopter Polish dries to a purple film, but it does so quickly, so you can always see where you need to buff.