I'm thinking about mounting a box of some sort above where the spare tire mount usually is. There was a blog somewhere where a guy mounted a bike tight there (remove front wheel, fork going into the "tight" and mounts the bike safely there). I'm still thinking a folding bike (a rad mini electric flooding fat tire bike to be exact) to replace my motorcycle for trips.
Any thoughts on a container designed to be mounted on like a garage wall maybe? I was thinking to back the fiberglass she'll with plywood on the inside (accessed via the rear hatch and up). Ideally a door would hinged to open.