Great idea you have come up with for the bending of pvc.

I am wondering how well you can glue pvc to plywood. If you can't, I would go back to pvc flat stock and use the regular pvc glue that actually melts the stuff together I think. Maybe after you have your trusses glued into place on your frames stations, you could lay them flat down on a table and with a router and jig, you could cut exact cut outs to fit you 1" longerons and pvc glue them into place. Just a thought.

John