Our favorite place to sleep on Que Linda is the forward berth.  However, it was very annoying, in the middle of the night, when the plug, which drops down to make a seat, would slide aft and drop down into the lower position.  We solved this problem by bolting a cleat near the top of this seat well, which engages the wooden strip already screwed to the bottom of the plug.

Details of the shim and the cleat are:

The shim and cleat were 8 inches long and made of teak.  They were bolted (using (3) 1/4″ screws and locknuts) through the vertical fiberglass surface forming the forward side of the seat well.