I've thought about it for the Bronco, which of course has a fiberglass half-room at the rear. For some reason, its easier for me to envision cutting and working with fiberglass than metal.
I've thought of a mini-earthroamer configuration, with a bunk above that folds over out of the way to give headroom from below, and back for a sleeping platform. If you've ever seen a VW Westfalia, you'll know what I'm thinking of. The flippy part would be so small and light as compared to a Flippac that I don't think any spring assist would be necesssary. The flippy part of a Flippac is 5' x 7', while i'm thinking of something like 4.5' x 5'.
I'm convinced that I could make one, make it waterproof, and even make a passable tent canopy, but doing it all so that it isn't as ugly as sin is daunting.