How do I take kit supplied vacuum-formed parts or sheets and make a durable mold for making fiberglass copies? Nose cowlings, wheel pants, fairings, ect......

These are small items I would like to try and duplicate, usually found in rubber powered kits. If it is simpler to accomplish this using a vacuum table I guess I could go through the building of one, but think makes more sence to keep just a small pattern and be able to paste one up with glass wouldn't it?