> I recieved another suggestion that the attachments would need some sort of
> flexability for shock absorbtion. I'm trying to imagine either a bungie
> connection to the deck of each kayak or some type of spring loaded
> universal joint in the middle of the cross braces. It shouldn't require a
> ton of movement, just enough to absorb the shocks. Mark

Research how arctic dog sleds are built. There isn't a bolt or nail in them, because they would shatter and rip apart if they were rigid. They are purely lashed, quite flexible, strong and as a result, survive and work well.