Here is today's progress.
First, I glued together a frame from plastic tube.
I fill in gaps and openings with Aves Apoxie Sculpt.
For the control surfaces, I glued two strips of 1/16" styrene sheet together after coloring one with a blue magic marker.
After cutting out the parts and sanding the edges flat, this gives me a visible line through the center of each piece so I can ensure the shaped edges are symmetrical.
At the end of the day, I have a body, two horizontal stabilizers and a vertical stabilizer. The rider is from one of the HB-88 kits; he's either a scaling proxy for the planned rider, or I'll paint him up if I run out of time to sculpt a new rider.