You are wasting your time with plastic. Just use a steel drum or get one made of aluminum or stainless and be done with it.
Have fun with the vacuum surfacer, it is nothing like you imagine, and I can't help you on a patented item.
Those rigid vacs are built for CFM, not lift. The small pool hose will restrict it big time and shorten the life. The lift on them are not sufficient for a vacuum surfacer unless you keep the hose real short. And I mean SHORT, and make a small surfacer.
I can sell you a vacuum surfacer for a better deal than you could try and make one.