Hello, I've read thru the site about making a throw away mold. I'm sculpting a helmet and it needs to be very smooth. So I know all about the silicone caulk and soapy water method for the mold itself, but what of the throw away helmet? I don't really want to use my smooth cast 300 for something that isn't the final piece, but I am going to (obviously) need a material that can be sanded and tooled and possibly sculpted upon further. Any suggestions, or should I just suck it up and use resin? Thanks!!