Photo of the cam cleat I use, placed on the inner side of the box. This enables the boards to be lifted from the opposite hull, cleating immediately. SS plate under it is to prevent wear on the edge of the timber from the 3mm lift line.
Line ends in the c/board hole, i.e. single purchase. Some bring the line up to the deck on the outer side giving a 2:1 purchase, but more line required and pull through.
A small piece of quality (rubber) non-skid tape placed on the side of the board at a strategic point at the top creates sufficient friction at the deck level to hold the board down. It only need a quick pull on the line to break that friction and lift the board. Keeping the line cleated at all times, even when down, prevents the board falling out of the case in the event of capsize.