[wmgeorge]

I used 5 Ply birch .500 for the base and then overlaid .750 best grade of MDF. It was special order both pieces because I wanted the full 5 ft wide. The tracks are spaced 8 inches on center but should have been 6 inch. The 5 ply holds the sheet metal flat head track screws better than straight MDF. The stack measures 1.260 as the MDF was metric. Your steel would need to be either angle or square tube to be an effective brace.