I'd suggest cleaning all surfaces you want to paint with a solution of T.S.P. (Tri-sodium Phosphate). You can buy it at any store that sells paint. WEAR HEAVY RUBBER GLOVES because it will eat the flesh right off your hands. After a good washing with the T.S.P. solution, rinse the surfaces with clean water a couple of times, then let them air dry. I've painted quite a few vinyl-clad walls, and have gotten better paint adhesion & coverage when I primed the surfaces with "KILZ" (also available anywhere that sells paint). Finally, use a high-quality interior wall paint and let it cure thoroughly before you expose it to rough use. I might also suggest that an eggshell or satin finish will be much more durable in an RV than a flat finish.
Good Luck, and be sure to post before & after pics!