well, i've been wanting to do this for ages now, so if you figure it out & your mould is still good after, i'm keen as!

my theory was, seperate the skin from the frame, cover the underside of the bonnet skin in a few layers of paper to sperate the mould from the original bonnet, and then put fibreglas straight onto that, ensuring you dont put too much resin on the fibreglass, and then once you have a thin fibreglass skin, remove it from the orignal skin, and then fibreglass onto what would be the top, making it to the correct strength & thickness.
are you heading for a lightweight frame for the bonnet as well? or just the skin?