I could use some tips for strengthening the airframe, and the best method to join some of the parts. I have some ideas, but I tend to overbuild stuff, resulting in unnecessary additional weight.
I have found many other sources for C/F that are usually cheaper than ACP, here's one of my favorites...
The usual technique is to use carbon strips embedded vertically into the surface of the foam. For a wing, the best place is usually the thickest place on the airfoil, top and bottom. For the fuselage, do the same along the length in a few places. Besides adding regidity, it will help tie the different modules of foam together.
In the first pic that Typicalaimster posted, you can see the concept demonstrated on his wings