Cobra Body Fibreglass Question!

[Ant]

On my Cobra the bodywork is very authentic in most areas, but like a lot of kit car manufacturers it has flat body sills, I think this is because its easier to mould, and most owners prefer "sidepipes" which hide the sills

I intend on putting some shape (1" deep) along the middle of sill tapering to the front guard, but my problem is I only have a relatively small 2 - 2.5" radius curve to bond to, and I am unable to go around the back of the sill as the cockpit floor is right down on the bottom edge of the sill!
I have contemplated using urethane foam bonding onto the sill leaving enough room to flare/finish the job on the outside, and shaping it, against an alloy sheet which will form a temporary backing edge to glass against, I could use either epoxy or polyester resin.

I realise my body chassis is unique and know one can really give an opinion without seeing it. The issue might be fibreglass cracking or delamination, but the body has two chassis mounting points each side of the major part of the proposed modification.

Hope all that doesn't bore you to death, and of I could afford a Shelby or Kirkham I wouldn't have this problem!!!