Here's a link
to the installation I did for solar on our TT. There were a number of folks who provided input on the attachment of the panels to the roof. In the end I used butyl strips under the feet, high helix screws into the roof and then applied Dicor self leveling sealer around each foot. Finally I topped the feet off with strips of Eterna Bond.
For interior I try yo use Command hooks or the Velcro strips when I can. However, there are some surfaces they just won't stick to. For those cases I use these toggle screws
Hope this helps!