Absolutely check the length of the screws if they're going on an exterior wall, especially. Some time ago on Hybrid Explorer a member had a very bad experience installing a bracket for their flat screen. Oops!
Trailers have had valances and curtains forever. In our HTT, they were put up with screws into the paneling and no problem. We took the curtains down, kept the valances and added mini-blinds. DH used the appropriate size screw and plastic anchors and no problem. Are the curtains you planned to put up especially heavy? Suggest you check into the anchors or the double tape mentioned above.