David, I have an 04 2100sd. I assume you are talking about the boards and pads that fit between the seats in the open bow that allow the seats to become a solid "lounge" pad.
Mine are at least 3/4 thick and made of a plastic or composite. Very dense - read "heavy"- even as heavy as they are, they still bounce in much of a wave at speed. For that reason, I would keep them heavy... The right bounce in the right wind and you might have a pad and boards bouncing off your face :-). My pad also snap down. In the front, it snaps forward of the little cooler box and in the back it snaps to the bottom if the filler board.
My board is 2 pieces.
I could take pictures and trace them for you if I were home as they are in my garage...but I am out of town for a month or so....missing boat season.....
FWIW, I don't use this pad often because I usually have more people in the boat. If it is just the wife and me, it always goes.....:-)
I hope that helps, and if you can wait a month, I can send you a traced template......where are you? My home is in the Seattle area. Right now,though, I am in northern michigan, with Lake Huron out the hotel window and me with no boat and lots of work to do.......:-(