Re: Wanted: 3/4" or thicker HDPE sheet
if you are open to other choices.
trex works well. just put it on top of the wood rail.
that pvc plastic 1 by 4 or 6 trim boards slides as well. and holds up better.
and those plastic pads you buy just for the boat rails really slide even the large boat like you have.
and as you probably know, you have to keep boat strapped down towing and strap on until in the water or it can slide off easily.