Painting Travel Trailer Bathroom Wallpaper

It may be that the vinyl layer of the wall covering or it's adhesive is still off gassing. That would make it very problematic to paint. You may need to seal the surface with a compatible sealer before painting. There may also be the option of removing the wall covering completely and starting from an uncovered surface. That also, may be problematic, as some wall board in TT's have the covering integrated fairly tough onto the underlying material.

Wish I had a fool-proof method to recommend. I have successfully painted wallpaper, using an oil based primer, like mentioned.