I have had plenty of bouncing too, and the only breakage I have experienced was from a kayak being shoved too far into the bed....
the conversation went like this

me: "hey dont shove that too far, I think its too long

SMASH, Tinkle tinkle tinkle

friend: uh... think I might have broken the window

Me: yeah, I think your right...

nothing like lots of sharp glass around expensive paddling clothes...


I would be sure to bolt it to the bed rails and NOT use the clamps, my cap seemed to flex way more when I used clamps

Jeff