A couple of thoughts.....
- Both VHB tape and epoxy have been used to hold panels. There have been some failures reported. I'm concerned about the bond between the gel coat and the fiberglass. Drill a hole in the shell and notice how the gel coat separates.
- if I used bolts and a sealant (butyl, rubber, etc.) I would double nut the bolts with a lock washer between so things don't come loose.
- with a permanent install the trailer may out live the solar panel
and at some point the panel will have to be removed. Not your problem perhaps but you do risk being the subject of a future post.
Good luck and don't forget, we like pictures. Raz