x2 agreedWithout prior experience moulding body parts, you're probably looking at several hundred hours of work to get this project from concept to finish. Expect to build a few prototypes in the process.
It's easier to start with a similar shaped object and build a mould off of that. Consider buying a CSL lid, casting it in fiberglass and resin, fill with foam and shave/add to that as your frame.
everytime i've seen a project like this one taken on the OP basically says the work took much longer and cost more than had they just bought a csl trunk (and modified that).
over the years i recall two that were completed,(both experienced bodyshop guys) one in europe and one from a guy who planned on selling them in texas?
if you don't have experience with this type of work be sure you know what you are taking on and have the time for. goodluck