Bill (Bornfree) My perspex, or maybe they're polycarbonate boards are 12mm thick and have been inadvertantly sat on by my 110k friend and they bounced him off. I think they should be as strong as 12mm ply, but I guess we'll only find out when the time comes to test them in anger
I too worry more about the strength of the timber channel that the boards slip into, they don't seem like they'd take too much to punch inwards for a theif, or a big wave over the stern.
Michael.