I was taking my kayak racks off for the season and noticed they where a lot looser then the previous seasons, and noticed the aluminum has cracked in the one pocket in the corner! They are just held in there with a bolt to stop them from moving around.

 

My backrack did a number on my 15, the J bolts started to pull right thru the bed wall. I never even actually used it for any thing except holding up some back up led light pods. I sold it instead of installing it on my 18.

 

I suppose it's the torquing of the frame that flexes the bed? I have a rack but the two pieces aren't connected front-to-back, just standalone 2-post racks. I don't see any damage (yet).