[ecomodded]

With a mini car maybe a mini boat tail.
A glorified Kammback.
Say 3-4 ft long, attached in such a way as to retain a functioning hatch.
Having the bottom shaped around the bumper & free hanging.
Constructed using your favorite ecomodder's proven technique.
I like the idea of mocking it up in cardboard, to help develop a good design and address the fabrication idiosyncrasies, of which their could be many.