Berth Board
I'm not sure what material they used on the original but my previous '80 H30 had a teak looking solid board about 3/4" thick for that berth. The board was the same length as the port settee and fit snuggly inside the raised edge of the settee. The width was slightly less than that of the bunk and partly determined by the clearance of the fully opened bunk. There were cut-outs on each free corner to clear the nav station and the bulkhead table when swinging the board into position. There was a full length piano hinge supporting the board. There was also a substantial piece of quarter round on the bulkhead for support and a triangular piece of teak that swung out to support the bunk near the nav station. You could probably use some 3/4" plywood and fabricate a reasonable replacement. Aesthetic considerations are up to you since the board is hidden most of the time. There was also a separate two-piece cushion for that berth.