My first voyageur canoe had hard plywood seats with a thin (very thin) insulating pad on top. (original classic voyageur canoes had only a narrow flat wood bar thwart to rest your butt on). Difficult to take for an 8+ hour race. We looked forward to the ADK-90 portages as a welcome break from the seats. The voyageur I next paddled and on the marathon Yukon River races was captained by a hospital worker. It had hard carbon fiber seats. He was able to obtain a large bed size gel pad that he cut into individual seat sizes. Beautifully comfortable on the butt all day and night. Our ground crew sewed cases and handle straps for them. The problem was they were heavy. So heavy they would sink if dropped into the water. But since there are not any portages on the Yukon races, they worked perfectly for our maximum paddling day of greater than 24 hours without taking a shore break. Since then I have discovered blue honey comb gel pads on Amazon that work great. Much lighter, but still somewhat heavy and add a lot to the total weight percentage to a 14 pound bushwhack canoe. The other main problem of how to secure the pad in place on the seat or elsewhere during an overhead carry. The Skwoosh canoe pad is fairly light, comfortable and small, an works well for a solo canoe.
