Thanks for the ideas. I can picture the leading edge of the head of the board needs to be wider than the trailing edge of the board, because when it is in the up position, the trailing edge is closer to the narrow top of the trunk.
I'm going to build up the head of the board, and give that a try first, so I can keep the boat race-worthy by not closing the trunk opening beyond the 1 3/8ths limit.
