I have an old garage door that has segmented panels. The panels look like some kind of mdf or hard board, but they have begun to rot. The wood holding the panels in place is fine, but 2 of the panels have rotted & need to be replaced. I haven't disassembled the bottom of the door yet to determine the thickness of the rotted panel material. Does anyone know exactly what that material is, how thick it is, & where I can get replacement material & how best to treat it to prevent future rot?