Great Planes Building Board Modification
Daywalker, when you fasten the board to the aluminum frame, the warp should be gone. Use self-tapping screws 3/4 the board thickness. Drill thru the aluminum bar, enlarge the bottom hole so that a flat head screw (with washer preferably) can be fitted thru with a magnetic screwdriver. I used three screws per bar, but you could increase it to four.............