Finally getting back to this one after the holidays and family commitments.
I've been learning the ins and outs of vacuum forming and its still not completely to my liking, but many times you learn by doing. I just don't like wasting a lot of styrene sheets trying to figure things out.
In my first attempt I made a smooth part for the bottom of the fuse. After some trials, I was able to make a useable part from 0.020" stryene.

Having gotten this far, I added wire to the mold to simulate longerons.

And formed another useable part from 0.020" styrene.


I used a lot of 0.010" sheets trying to get a good part, but concluded this is too thin to vacuum form well.
Next I will try a vac formed fuselage turtledeck, which is a more complicated shape.