Enclosing the space behind seat on TF

[OrrieG]

I have found a bunch of photos of finished truck interiors with the area behind the seats enclosed to match the inside cab curves. I have not been able to find any threads of information on how to build that except for plastic panels for sale by aftermarket guys. By experimentation I have found that 1/8" masonite will not bend the radius with out breaking. I am thinking maybe heavy card board as a form for building up fiber glass? I can make some cleats to mount under the window where it kicks back and for the floor.

Any ideas would be appreciated. Thanks Patrick