Couldn't you cut the cradles from 1/2 inch plywood and make each cradle from two 1/2 inch plywood panels separated by 1x2 (on edge) to give 2-3/4 thick cradles shaped to the bottom of the hull. Attaching the cradles to the crossbars of your racks is the tricky part. It's going to vary dependent upon the rack design. You could put stringers between cradles resulting in one cradle assembly that attaches to the rack crossbars.

> Does any one have any good ideas about building kayak saddles
> for the top of my car?