RE: Goldberg Ultimate 10-300 build
i use a similar building board, but shim the working surface till it's a flat surface and not warped. don't expect the door under your building board to be perfectly flat. set your building board on it, set a 4' level across your board front edge and rear edge, then diagonal. use thin pcs of balsa to shim (1/32" & up) as necessary to make the board even w/ the 4' level. i build on hdo particle board, i have clamping pads of plywood i screw over the spars (into the particle board) to hold tight to the board, i never liked pinning because the spar can slide around. then i screw down a balsa building board for working on the tail section.
jon b