I have a wooden up and over garage door that is badly rotting. The metal frame, subframe and opening system is fine, so I want to build a new wooden outer cover to fit to the subframe. My question is what to use for panelling, currently it is panelled in ply but I wondered if tongue and groove would work okay and if I could get away with using the thinner 8mm stuff for weight reduction rather than the more secure but heavier 14mm...would this be too heavy for up and over?