Thanks. I'll look into that. It feels like the bent up edge is more comfortable because the pressure is distributed more around the side. I was thinking of intentionally cracking the other side to test. This makes more of a contoured seat instead of a flat seat. Unintentional design modifications sometimes work out in the end. That is a pun but I didn't know it until just now. Maybe I can make a contoured seat using thin plywood and the carbon twill you suggested.Did you think about a adding 2 layers of carbon twill to your plywood sheet ?
it would definitely avoid the crack, take a look to the vids of DIY skateboards on YT