What can I use to hang things on the wall?

I’m looking for the best thing to use to hang decorative items on the walls. I have several picture frames and assorted signs that I have displayed on my wall, but they keep falling down. I assume it’s due to the wonderful Missouri humidity that builds up inside when the RV is not in use. I have tried Velcro strips, command strips, command picture hanging strips, they all fall eventually. Any suggestions?