Some of the newer, Victorian wallpaper that I purchased has very tiny type on one of the edges recommending that the user spray the paper with fixative before applying the paper. Several years ago, I participated in a Web conversation where someone ranted about NOT using anything that a person printed on their computer printer, because it faded too quickly. Well, I installed the above paper about 18 years ago, and look at how it's faded. (Alicia had a couch in front of the area where it is darker.)
When I got into the discussion about not using computer printables, I contacted HP to find out what they predicted would be the longevity of their printed inks. The tech who spoke with me said it's hard to tell. He said use acid free paper for starters. Then he said, once it's dry, spray it with fixative. Their research had indicated that this would help reduce ultraviolet light degradation.
I also have used museum quality glass in areas of my dollhouses and room boxes where I can put real glass, because most museum glass also offers some protection against the damage of sunlight, too.
So, long blog short - spray your wallpaper with fixative before you put up any paper. You can get the fixative at most any art supply store.