I like having mine, on the top of my TC. My rack is used for 3 of my 100w Solar panels. I have two unistruts attached to the two rails, by the sliding nuts, that Carb Cleaner (posted above) shows. That way these panels are are protected by the edge of the Unistruts, thus reducing even more the height above these rails. Not sure why someone would want to use those Mounting Feet (Yakima/Thule?) and skinny crossbars, since they are so many $$$$$$$ and does not supply the support a Unistrut does. Plus you are putting any item that much farther up in the air, to reduce MPG and create turbulence and stress on the connectors.
I have a combiner box, installed directly above one of my inside cabinets, to allow a straight drop down to my moved Battery box. I have two AGM batteries mounted in a cabinet, as well as cables, controllers and switches. (300w(3x100)-240AmpH (2x6v) The former outside battery compartment is just used for outside storage, now. The solar cables don't even touch the roof, routed along Unistrut to Combiner box. Yes, the Racks serve me well. (Why are they called Maggie Racks?)
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