When I was lobstering, I used a heavy electronics mat that was used on work benches. They had a grounding material inside and were the right weight and size. I'd unroll and toss 2 4' sections over the gunnel. Not a scratch.
I built a table out of starboard that mounts along the gunnel to scotty bases. Then I ran a starboard section 12 inches down the outside of the gunnel to protect it. Works great and is a solid platform for placing traps. With the benefit of not having to bend over to the deck to empty crab out of the traps. I'm getting old!
I use 2 old hot mats from the local PUD that have been culled out, only cost a couple bucks work great, super light weight and really durable, had mine for about 10 years