Mdf is the way to go here. doors are not that strong, and aren’t going to hold up to the abuse of routing. most of them are just luan over cardboard. metal will be too heavy and is definitely going to flex under its own weight over 10′. Which I don’t know why you need 10×5. Shouldn’t it be 9×5? mdf can be found in 9×5 or at least 9×4’1″ depending on the source.