if the paper is hung properly, the humidity shouldn't be a problem... I love wallpaper in powder rooms!

are you planning to hang it yourself? you probably should try to sand the walls so they are at least pretty smooth-- it would be hard to use the smoothing tool if there are too many bumps, etc... probably would affect adhesion too!

if you're hanging it yourself and you're not too experienced, I would get an overall pattern that is a little busy that will help to mask little errors-- not too many areas that need super careful matching ... and don't get too linear of a pattern. putting crown at the top is great way to mask any issues you might have at the ceiling! (esp if you put it up after you paper! that way you don't have to be too careful at the ceiling! :)

I'm not sure if I will hang it or not. My dad is a builder so he's hung it before. I agree on the pattern lol. The walls aren't awful, just not as nice as I like it, and painted. We took down 80s paper and repaired them. It has 4 inch crown. Thanks for the advice :)

Thibaut is a good place to look.

Thanks Pal, I will check it out :) I definitely want something nicer than what the home improvement stores offer

Paint stores often have lots of wall paper books, and when you just need a little, like for a powder room I've even found great stuff at The Rebuild Center

Just be sure to use a wall paper primer/sealer or else you will never get it off and you will curse the day you ever decided on wallpaper. I find it easier to remove the papers labeled "strippable".

Love Wm Morris papers.

Here's another.