Vaccum forming is fun, isn't it?! I've made quite a few parts with my homemade machine using the same book pictured at the beginning of this thread. My 5HP shop vac has always had plenty of suction to pull just about anything I would want to make. The key I found was finding the sweet spot during the heating process. Too cool or too hot was what would cause problems. Attached are a few pics of things I've formed and their molds for my Space Shuttle project. The shuttle main engines and OMS engine bells as well as the heat shields and engine nozzles on the SRB's are all vac formed.

Dan