I wax it every year including the vinyl graphics. It doesn't hurt them at all unless you rub very hard in one place (like trying to remove sap) and then it will lift the color some. Otherwise mine have suffered no ill effects of all the waxing (including peeling). The corners of the TT that get black streaks are waxed 4~5 times yearly (incl graphics) because it seems to make the black streaks easier to remove.
I think keeping the UV off the trailer keeps it looking good and this is especially true for the stickers.
Just my experience with my 10 y/o TT!
EDIT: Maybe sun+wax on graphics makes them crack? Just a wild guess but wax alone sure didn't hurt the cheapo stuff on my TT.