As I sat sanding by hand I started thinking about other possibilities for producing shapes in this way.
You're probably aware of this technique, but in case not.....
Back in the car audio boom of the early 90's, I would stretch polyester cloth tightly over a framework and soak that with fiberglass resin.
Then hand lay fiberglass over it for strength. (I like the things I make to be strong enough to stand on).
I've seen others use only thick fleece without using any fiberglass mat, but I've never tried it.
Do a google image search for "custom fiberglass enclosure" to get an idea of what shapes you can get.
(don't want to threadcrap with pics of things other than your cab)
Using everyday objects as molds for the fiberglass can yield cool results too.
If building your cab, I probably would have got a big ball from toysRus and hand laid fiberglass over it.