I don't think a cutting board in place of the metal plate would be rigid enough to support the weight of the seat and driver. It isn't mounted flat onto the slide rail, so the plate has to be strong enough not to flex (2nd pic). The reason that you don't mount it flat is to be able to slide seat back and forth. I used aluminum mainly because it's a bit easier to work with than steel, although a steel plate could be a bit thinner, I believe Newty said his was 3/16" thick. Hope that helps.