A new Yakima or Thule is a bit pricey for me, but I found a Craigs List one off a Mercedez (sedan rack) for cheap. (I only need it a few times a year.) This had a different slot system, using four long M6 threaded bolts which enter the (Mercedes) crossbeam slot via a removable side cap. With a little grinding of the heads, they fit the TRMR Series 10 slot fine. Once correctly positioned, the roof box sits down on them and is then secured from inside the box with plastic hardware and M6 (hand) turn knobs. I'd rather not remove and re-install the cross bar to insert the M6 bolts every time, so I got a few stainless T-nuts, four stainless M6 threaded rods (250mm), and some stainless lock nuts. The stainless M6 t-nuts are in the TRMR slot permanently. I screw the threaded rods into them, then secure them in their (proper) places with the rubber washers and lock nuts and mount the cargo box onto them. That way I can remove the vertical mounting rods when not on a major trip, and I don't snag any car wash gear.
Speaking of the car wash, I have found that the rinse does not chase the wash product out of the front crossbar sections very well (I have the Heretic 40-inch light on a 4DR hardtop), and soapy water trickles down after I leave. My car wash chain ($30/month for unlimited washes!) has a clean-cloth station outside, so I just take a little time to wipe the truck clean of droplets.
Getting back to roof mounts, all my crossbars have four 1/4-20 stainless T-nuts in them, permanently, and two have a pair of M6 t-nuts (for the cargo box), also. I have an assortment of 1/4-20 threaded rods, different lengths, 1/4-20 lifting ("eye") bolts, etc which I use in different combinations to secure recovery boards (6-inch rods for those), tie-down boxes or other gear as needed. Very flexible, and so far, works.
Look into this, TrailRax, and test them out. Could make a nice accessory package.
