I just tried a neat molding trick.
I wanted to make a master to pull a canopy on a vac-u-former. Normally I would carve it out of wood but I wanted to try something different.
I made the part out of foam using a hot wire and sandpaper. Then I took some Kleen-Clay I use for two part molding heated it up in the microwave so it was softer and pressed the foam part into the clay.
I let it harden back up a bit and pulled out the foam plug. This left a cavity the same shape as the plug. I poured in some liquid plastic and let it set up and BAM!!
I have a part in hard plastic I can use to pull the canopy from. Just a little sanding to smooth it out and I will give it a try. Cheap and dirty one time mold. BD.