Wet sanding is fast, easy, and works well on flat surfaces. In corners etc, it's difficult at best. I think there is a liquid product sold in automotive paint stores that etches paint to remove the gloss, in preparation for repainting. I would contact a local automotive paint supply shop and ask what they offer. If you don't have such a store near by, do a search on the web.
Such products might be rough on certian metals, so understand that some of RV wall and door panels are made of a combination of metal trim & rivets, with fiberglass.