Update-o-rama...
I sturdified the structure by mostly enclosing the back end with more cardboard & tape and carefully peeled it off the car tonight. The "release agent" (tin foil) worked quite nicely.
All trussed up with cardboard to hold the shape for pulling it off the car & glassing in a lip & underneath
Showing the "release agent" - tin foil.
Spent time trimming the raw edges, added a glass & cardboard 90 degree lip to the trailing edge and worked on glassing the underside (until I ran out of glass cloth & applicator sponge brushes.
I was surprised to read today that Craig Vetter's latest motorcycle streamlining project is not going to be fiberglass construction. He's going with bulkheads/skeleton and a plastic skin. Composite construction is too expensive and difficult to ship is his reason.
I figure the total cost of the Kammback will come in around $100. Most of that will be resin & glass cloth. (I also didn't try very hard to find a cheap source for it - just picked it up at Canadian Tire.)