I've found that Ace bandages worked like a charm. (Used what was handy). Spritzed the outside surface of the sheeting with water and formed it using the bandages to hold the pieces in place, then used the bandages to hold the pieces after glue was applied. I was about to use hold down straps, but this is a much better method for this application. No big buckles to gouge the wood.

Good call RCKen, this should be in a book somewhere.
Just one other question, why would a person use ammonia in the water used for curving wood?