I purchased the Thule kit that's sold by Ford dealers, you'll find it on accessories.ford.com as Racks and Carriers by THULE - Removable Roof Rack, Aeroblade at $485. It's a complete set with four different items: Load bar, Foot Pack,Fit Kit, and locks.
I put a big roof box on it before a 3800+ mile road trip this summer, and it stayed secure the whole trip. I did create a couple of scratches inside my door well before I understood how these were supposed to go on, but other than that they worked flawlessly. You can hear a little whistling as you cruise 80mph on Idaho and Utah freeways if you keep the sliding cover for your moonroof open.
Yes, these are expensive, but I more than made up for it in gas savingsby taking this road trip in my FFE instead of the minivan.