I used 3M VHB tape to mount a solar panel on the roof of our former Casita, using 1" square aluminum tube as spacer/mounts, and never had a problem through all seasons and conditions (UV is intense at our 7400' elevation). I used it for other projects as well - shelves etc. Used fresh, with proper surface cleaning, the tape is very effective. When I had the dealer install a rooftop solar panel prior to delivery of our new Airstream, he was not willing to use the tape and drilled/riveted the mounts. No problem with that installation, either. For careful DIY, I wouldn't hesitate to go with the tape. Note, however, that I continued to use the roll for other projects, and after two years (stored in zip lock bags) the tape did not bond as well. It does apparently have a limited shelf life.
Joe & Joan Donnaway