Another minor update. I haven't been home much lately, but decided to post this little snippet.
The templates Elvis provided (thanks again fella!) were for 1/4" sintra, and I am using 5mm as it was all I could get hold of. With this in mind, I needed to adjust the measurements for the sides of the medkit to end up with the proper 3 1/4" depth. After measuring the boards I have for the front and rear panel, which were not the perfect 5mm as you would hope, I determined that my side peices would need to be 73mm wide. As such, I made up this alluminium guide for cutting.
My intention is to cut the PVC board into strips which I can then cut to length as needed to build up the sides and internal structure. This should help create uniform depth ensuring the whole kit ends up square (though not square in shape!) I plan to mitre the corner joints and also reinforce the internal corners, which should allow me to round them out with minimal need for filler, though some filling is inevitable!
I hope to be able to obtain some shells from @hms, to build into a very screen accurate piece, so this build will end up being my con-kit, screen accurate in dimensions and apperance but alittle more idealised in terms of how it is put together to make it abit more robust and "usable".