Francine..
My trailer doesn't have wallpaper in it, so I can't comment on a
fiberglass trailer, but my childhood friend's parents have a 1996 Jayco Motorhome that her father has replaced the dated wallpaper in there a couple times. Having done wallpaper in my own home on several occasions, I asked him about it - he claims to have installed it the same way as you put it up in a home, paste the wall, the paper, and he put it up. Looks great too!! He's a pretty handy guy....