RE: Bubbles in poly ply?
Poly Ply is a very thin epoxy fiberglass board. It is available in several thicknesses, but you cannot heat form it, like that.
How about punching or drilling a hole to clear the screw head, and then bonding a butyrate (canopy) plastic bubble to the Poly Ply?
Harley Condra
BVM REP
Team Jetcat