The light trap on these boards is a simple rabbeted edge. In the beginning of my trials with home-made boards, I attached a piece of black foam-core board, smaller than the real board by about 3/4" (to allow a 3/8" setback from each edge) and with a large enough center whole to allow the flange to fit through and tighten down on the board itself. In my case it made no difference to the final function, so I stopped doing it. As long as the board doesn't wobble in the standard, I say good enough... but then I'm a lazy bas****. Your results may vary. Try one with a paper negative if film is precious. I had enough donated, out of date film to play with until I got it right. Fortunately, there was never a problem.