Hi Steve - its for fun too and I get what you are saying for cost.
I will be just wet laying GRP. I did look at CF and infusion bagging etc but way too expensive for both materials and equipment for a 'one off'.
I have just spent £150 on the materials and this will do both the mould and the actual panel. I will not be making a mould of the underside as yet. I will go 250gsm the 2 x 450gsm with strengtheners in the right places. The boot that I am doing first is held on with pins and springs and has no hinges. A skin for this is fine and will get good height from packing out the pins. If I am not happy I will mould the under web and then bond the two together.
The bonnet may be a different story though. I will probably have to double that up for strength as it is such a big area.
The boot lid I have for the plug weighs 14.5 kg. I am sure I can at least halve that. I hate to think what a bonnet weighs - they are a beast.
The doors are currently steel but all that remains is the top frame, outer skin and a little of the door outer perimeter carcas with 3mm poly windows. I may GRP the rears as just a skin, don't know yet.
If I bought a Smith & Deakin bonnet I would not be too far away weight wise from a steel one but they are not into the weight saving that I am. Good bonnets are very difficult to find and command good money as are rare. I will put my money into making a good GRP one and save weight too - it keeps me pottering in the garage too.
I have only had experience of a MK2 Escort GRP bonnet and was quite impressed at the strength and rigidity and the weight of it.
Why do we do theses things? Because we want to