Thanks Marc for a very informative answer. I like the idea of a single solution that caters for all my perceived needs - I will be taking a longer, better look at the PMDX site.
Skippy - I think that Euro screws and the Confirmat screws I used are probably one and the same thing. (see picture)
The idea of using flat sections was to simplify the construction and yes, a monocoque would be much stronger but I figured that a well thought out alternative would be much easier to make. I am definitely thinking of a sandwich structure but not yet determined what the core material will be. I use Rohacell, an acrylic foam, for the models. It is extremely light weight 31k/M^3, 51k/M^3 and 71k/M^3 available yet it has very good compressive strength. If the core is reinforced locally where the pieces will be bolted together, I think it will work OK. However, I am a long way off that yet.
When considering composites, it is worth noting that you really ought to use just one type of fibre and not mix them. Glass and carbon have a quite marked difference in coefficients of expansion and considering I am using prepreg material, baked in an oven, when mixed the results can be quite alarming. I know because I have done it - if you want panels like bananas, laminate one side with carbon and the other with glass - you will be quite amazed at the outcome.
Carbon prepreg is about twice the price of glass weight for weight but you have twice as much fibre in the carbon so there works out to be not too much significant difference if you compare strength to strength.
Mike