: Does anyone out there have experience using PVC pipe for strongback...

As a seasoned amateur telescope maker, I can tell you that PVC is one of the first tube materials newcomers to that hobby think about. And it is without a doubt one of the very worst of options. As Malcolm says, flexure is the problem. I would avoid it like the plague.

PVC pipe is manna from heaven for lots of things, but never as a rigid structural material.

My $0.02
Kurt Maurer