[Jon]

Tim I use to make moulds for fibreglass many years ago. We always used plywood and apoxy resin filler. You could build up the layers of the mould with plywood, sand off or plane the external corners. When you have a reasonable basic shape, spray the item you want to copy with wd40, mix a load of car body filler and push it into the places that you couldn't shape with the plywood and press on your copy panel and leave until the filler has gone off. Its a tedious job now of sanding and refilling until you have the prefect shape and fit.