I'm restoring the door to my dumb waiter. The door is 1" thick, plywood core, tin exterior (1/32"); the door is original and dates back to 1939. I want to make the door completely flat, then paint it, but I'm not sure how to fill in the recessed panel such that is does'nt warp or crack later. The panel is 36" x 7", 7/8" deep.
My first thought was to use something solid, like MDF, to fill in most of the space, then use fiberglass or metal-reinforced bondo to fill in whatever space remained; apply another coat of fiberglass/bondo on the entire face of the door, sand, paint, done. Is that a good solution?