I needed to make some flap parts that were all identical so I followed the instructions from the EAA website and article about low cost Hyroforming which really is rubber sheet forming. It worked well and was quite fun.
I love playing with that method... especially since cessna think's $1000 is a ok price for a little rib that should cost $50... you can make the tooling and many for in a couple hours....
I buy Corian counter top material off Ebay in flat rat boxes, for making my dies.