Geneva Auto Show: Edag Biwak recalls (some)Thing - Autoblog
How does the vertical height of their back door compare to the vertical height of the stock hatch?
It's a more complex build with the fenders and rear bumper included; but you should be able to reproduce the top contour with an additional seam. Consider a clip that reaches forward of the hatch opening sufficient to get ahead of where it starts to fall off.
Edit: some other stuff EDAG does is pretty far out there, e.g., Genesis; but here is the relevant contour on their
Light Car Concept.
Black under pinpoint lights doesn't photograph well. The pictures load better down in the comments. It's made out of Basalt fiber!