I have both Yakima cross bars, which attach to the rails on my Disco roof, and Thule bars which sit high and mount into the rain gutters. I use the Yakimas for my ski rack and the Thules for my travel box and carrying lumber, etc. My Thule racks are tough, easy to install and work great. The only reason I have Yakima is because of their round bar--I can roll my ski racks down and drive into my garage.
I've never had a lick of trouble with the Thules.
Go to rei.com and I'm sure they'll have the info you'll need.