The washboards from Multihulls Direct are made of 6mm Acrylic, and slot into a 6mm groove fashioned into the companionway. The trouble is 6mm acrylic has quite a bit of flex, and a good kick would easily dislodge them. So I made some new ones.
In order to fit the existing 6mm slot, I epoxied two sheets of 5mm foam together with an offset around the edge. A layer of glass tape where the overlap protrudes, a layer of 600gsm glass on each side, the edges routed out and backfilled with epoxy, and I have an extremely sturdy panel. Also, unlike the acrylic, it floats.
The lock is a Mobella which was not expensive, fairly easy to fit and the smooth edges mean it would be very hard to pry open.