After spilling the tray contents out of my box all over the ground for the umpteenth time I came up with a similar retainer pin system. But I use a long shank ball-driver wrench in the back that drops into an alignment block. To a casual observer, it is an inconspicuous "lock" mechanism and is useful as a tool so it's a multi-purpose item. I have enough other needless junk I carry in my flight box.