Jim Carter's upholstery material seems to be a good match of colors, grain, and stitching with originals (except he does not have the original-style gray/maroon for '54 seats). He would probably send you samples of material, if you asked.
Some people varnish/seal the back side of the cardboard pieces. Some people buy plexiglas or tempered/water-proofed masonite board, or luaun plywood (varnished) and cover it with material to match the seats.
Tim
