Can anyone give me any ideas for "bobbing" the rear frame rails and adding a roll pan to my 32 3 window coupe?

I would like to eliminate the exposed tank and frame rail sections from the rear of my Gibbons bodied 32. I would presume the only option would be the installation of a fuel cell in the trunk 0 so much for the rumble seat idea.

Does anyone know of a pre-formed fiberglass piece to fill the area for this type of modification? Any pictures would help.

Thanks!