I need advice from those that have mounted the Thule, Yakima or other luggage/cargo boxes on the factory rack crossbars. I have read from some others (not specific to Expeditions) that they recommend using thin foam between the box and the crossbar to eliminate knocking or vibrating and to use rubber tubing around the steel u-bolts to keep them from sliding or marking up the bottom of the crossbars. I have mounted my new Thule box in the garage to adjust the spacing of the crossbars and see how it installs and it seems very tight once everything is locked into place but I don't want to figure out different on a road trip beginning in a week. Thanks for the advice and suggestions.