I have a 2000 Forester and am considering purchase of 2 Rocky Mount Noose roof bike carriers. These carriers attach directly to the crossbars of the Forester factory roof rack. Is this safe? The factory crossbars seem pretty sturdy and the Rocky Mount rep says they'll mount directly to the existing rack. I'd like to avoid the costly Yakima and Thule racks, which require purchase of crossbars as well as bike carriers for the bars.