I'm getting scoot... no matter how hard I tight the thule attachment, the thing, at one tower in particular, the thule is scooting in the direction of 'off the rail'... kind of frustrating.. since I have two side by side.. the outer side attachments have to set on the rail outside of the tower... 

I've used some thin nylon rope to tie the 'attachement' to the tower, to limit outward scootness... but there is some angling of the attachment, like maybe it will just get bent... 

So it looks like I'm going to have to get some metal plate, get two holes drilled in it, and fit this plate inside the thules, just inside of the tower, drill through the thules (whole bigger in the thule than the metal plate?) (I want to stress the metal plate, not the body of the thule), and then use bicycle cable covered with clear plastic or similar... to tie down each thule, at inside each tower, to prevent outward scoot.... 

Of course I have more weight on the outer edge than inner edge of each thule, cause I was trying to limit or eliminate bowing of the bar... - - - though really, I'm going to have to get two more bars and four more towers...