I'd also ask if you're talking about painting the interior skins or the woodgrain vinyl coverings on the walls and furniture.
If you're talking about the skins, I'd rate paint as "last resort." (there are some 70s trailers in which I'd just HAVE to paint the bathroom walls, the flower-power thing doesn't work for me. Happily, the "cheap" line from the 70s used the same neutral off-white color in the bathroom as in the rest of the trailer.
The PO of my 24' Argosy replaced some of the woodgrain on interior partitions with very nice wallpaper, and did it well. He left the woodgrain on the cabinets and furniture, and the effect is very nice (IMHO). You get a lot of the original look without having too much of it, if you know what I mean.
The vinyl coating on the interior skins is very, very tough and it cleans up pretty well if it hasn't already been painted. When I was looking for the 28' trailer, it was always disappointing for me to find one that had paint slung all over the interior.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill