Hi guys.
After much thought and much doubt in what could be the best way to build the fuselage, I decided to do the opposite of what common sense dictates (not sure what to think of myself and my sanity). :wacko
My explanation: since, thanks to my prototypes, I already had the accurate measurements and profiles of the outer surfaces, why complicate my life and start working from a lower level that would force me to make new calculations for a sum of layers that give me a result that I already had?
Maybe not everyone understand my logic, but I decided to build my fuselage from the outside inwards. :unsure
The first problem was that is not the same folding a thin cardboard sheet that a 2 mm. thick sheet styrene. The edges of the styrene pieces need to be profiled in a particular angle so that the adjustment angle between them is correct.
To facilitate this, I designed and built a simple tool with a blade that I can set at any angle. Repeatedly sliding the tool along the edge of the pieces I can easily get the profile I need for a perfect fit.

The tool is built with 5 mm. thick foamed PVC, a screw, a wing nut, and of course, a resistant blade.
Can it be made easier and cheaper?
Using this tool and a small external rib structure, I've built the top rear of the fuselage and the window frames of the cockpit.
The pics:
01 - The angles I've calculated to fit the pieces.
02-03 - My profiling tool.
04 - Profiling tool in action.
05 - Profiled parts ready to be joined together.
06 - The droidstrip socket .
07-08 - Building with the aid of external ribs.
09 - Building inwards: profiled internal reinforcements.
10 - Upper rear fuselage almost complete.
11 - Cockpit frames.
Thanks for looking.
Rafa