If you need a flat panel, look for surplus aircraft floor and joinerwork pannels. These are available in 3/8, 1/2 and other thicknesses. They are hpneycomb with s-glass or carbon faces. You can find sometimes on EBay. There was a truck load for auction a few years ago and I lost the auction. Was bought by Advanced Vehicle Technology. Still selling it through their store front at www.avt.com I believe. You cannot bend a flat panel appreciably. On the other hand nothing is as stiff and light including anything you can make at home.