Idea for headliner backer board

[echo7bravo]

I am working on a 1986 K10 stepside for my son. There is no headliner or backer board. I know I can buy a ABS backer board from Brothers for about $200. However, my son and I are project oriented and thought about making our own.

What are everyone's thoughts about layering press and seal plastic wrap across the ceiling with excess over lapping the edges or where the headliner would stop. Then adding a layer of fiberglass to create a form. Does anyone think it would stay in place long enough to harden?

I was thinking of trying it. I would then trim the edges and drop it down. Could put it on a table top and add a second layer of fiberglass.