Yakima SweetRoll saddles are the best combination kayak cradle system/roller loading assist. To load your kayak on the roof of your car, just set the bow on the rear rack and push it forward while it rolls into place. Once your kayak is centered between cradles just tie it down as if the rollers weren't there - simple. Mounting the SweetRoll on your crossbars is simple too, just crank the knobs on the side of each piece and it clamps onto whatever style crossbar you've got (except oversized bars such as Xterra).