I just this week added a small panel to my rig. I used a classic rigid mono crystalline panel with screw down mounts. Using a stud finder I was able to screw into my roof trusses and with generous use of self leveling lap sealant under and around d the brackets I’m confident they won’t leak. My panel is only 80W which should be enough to keep my batteries charged in storage. If not I’ll add a second panel. Used all Renogy equipment with a 20A MPPT controller. All in was under $200 and it was a fun project. Also added a Trik-L-Start so the chassis natter can share the fun.