Great question. It took me a while to engineer the bracket and then I had to redo it to make the rack an inch taller when I stiffened the rack with some additional tube stock. It ended up that the final design has clamped very well and does not shift or loosen on all the trips. The extra piece of metal on the inside of the track was originally added to give me the extra inch of clearance, but in the end it actually created a better clamping method. If I weren't in a hurry the day I had to retrofit this, I would have welded the inner piece to the vertical bar, but the 3/8 bolt works fine for now. The outer piece of metal is stainless angle stock that I trimmed the lower leg. One lesson learned was that the angle stock has to be thin and mounted as high as you can so that it clears the doors. The only remaining improvement I would make is to adhere some rubber to the two parts that grip the gutter to reduce the paint rub-through.
This rack normally contains one 38.5 spare tire and a canvas luggage carrier with a full-size tent, 4 sleeping bags, pads, and a tarp, the shovel and axe, so roughly 200-250 pounds and it doesn't shift or squeek. I can easily sit in the rack when I am working on the luggage or lights and it doesn't budge.
Hope this helps.
