I've been toying with that idea for a while (since I got a bare frame), and I even started a thread to find out what the consensus would be, but it veered off-topic and some trolls jumped in... Anyway, I sketched out a body-shaped cage (just pencil & paper - not CAD), and I did a detailed drawing of the frame in preparation for building the cage, but I haven't gotten any farther with the idea.
My plan wasn't really a tube-buggy, but just a body-shaped cage on an eB frame using normal (poly) body mounts & a few pieces of original (repro) sheet metal and mostly plastic exterior panels (like flat-track cars).