I have a Yakima megawarrior basket with 18" extension for our Yukon. I had it mounted to the factory cross bars using the Yakima clamps, but the cross bars flexed too much with bikes mounted to the rack. I replaced the oem crosss bars with unistrut channel from Lowe's. I use unistrut u-bolts to attach the channel to the factory rails, and u-bolts with nylock nuts to fasten the megawarrior to the unistrut.
Sorry, I cannot get any pics, the rack is not on the Yukon right now. I have to remove the rack to store the truck in my garage for winter. The unistrut works well for me. I placed 2 or 3 unistrut washers in the u-bolts between the factory rails and the unistrut cross bars for clearance due to the arch of the roof. The unistrut channel is zinc coated, I scuffed and painted mine with black truck bed coating. Just google unistrut roof rack for ideas, lots of other people using it.
Sorry, I cannot get any pics, the rack is not on the Yukon right now. I have to remove the rack to store the truck in my garage for winter. The unistrut works well for me. I placed 2 or 3 unistrut washers in the u-bolts between the factory rails and the unistrut cross bars for clearance due to the arch of the roof. The unistrut channel is zinc coated, I scuffed and painted mine with black truck bed coating. Just google unistrut roof rack for ideas, lots of other people using it.