Next up, tail cowl shaping and fabrication: I usually buy a sheet of rigid insulation board, cut out a few squares and glue them together to form a block, and then cut/sand it down to shape from there. I prefer the rigid insulation board because it's cheap, sands down nicely, and holds up to some abuse but can still be cut easily with a carving knife. Hand-shaping these on the bike is one of the more purely artistic and enjoyable parts of the build process for me, but damn I hate working with fiberglass.
Rough cut
Sanded down to the basic shape I was going for
And the final form, after a lot of massaging:
Filling in gaps with some expanding foam to make sure everything fit to the frame nicely before fiberglassing
Used painter's tape coated with carnauba wax to help release the fiberglass part from the form -worked great! Would recommend several layers of tape though, the resin ended up seeping through and melted my form