Surface prep is a must
Tha wallpaper may have a coating, or at least ink.
Given the heat and other issues in storage one should avoid any peel and stick of any material with mass.
Unless the new tile is special I would suggest using some "fake tile" hardboard, looks like tile but is light and thin, goes on like paneling, strip off as much wallpaper as you can, rough up the rest, liquid nails and you are good to go.
If you want ceramic, then the wonder board securely attached then install tile.
Make a trip to a tile specialty store where they do this as a primary task, you want to insure the correct mastic and grout for the application, drive your MH there and allow their sales/installers to assist you in your choices.