Large diameter PVC tube, cut it in half, heat it up on the grill, once it's soft lay it on the hull with carpet in between. Let it cool, glue carpet to pvc, Bolt this to wood and bolt to the trailer.

Or do what Jake said.

I made some custom cradles for my a cat by laying carpet on the hulls and then carbon, epoxy over that. The connection to the axle was a pink insulation block covered with carbon and epoxy. Painted to match the boat. Probably the most over engineered, most time consuming, most expensive cradles ever made.