Headliner Shell Fabrication

My latest project is not an A-body, but rather a '56 Plymouth that will become a mild custom. There are so many creative folks on this site, that it just seemed the best place to get ideas. I hope nobody minds.

In place of the bows to secure the headliner, I'd like to fabricate a shell and glue a modern headliner fabric onto it. I'll probably use fiberglass for the shell, but I'm curious if anyone has ever done something like this before, and if so, what did they use for a mold?

I've been thinking that blocks of Styrofoam glued together and formed with an electric knife and a rasp might be one way to go, but I'm open to better ideas. Of course, the Styrofoam would have to be covered with plastic, or sealed some other way to keep the fiberglass resin from dissolving it. Maybe a layer of modeling clay on the Styrofoam would serve to seal it and also allow more detailed forming of the mold.
Author: GaryS