Wow neighbor!!! That is f-in cool. I have a nephew I'll be having to do that for eventually. You did an awesome job.
The por-a-kast is made by syntek. They are another of our many plastic resin providers, and used to be the most cost efficient. In recent years tho, Smooth-on has moved up. They are now less expensive and have, in my opinion, the better products. Especially when it comes to their mold rubbers.
I just cast my new helm out of resin. I started off by painting the first couple of layers in with a brush. Just to make it even and bubble free. I then slip cast it with the resin. I only put it in about a mouthwash cup sized portion at a time. and kept it moving till it set up. The resin is much nicer than the Fiberglass. Stronger too.
-Chris