roof racks
 

We just bought a low milage 2005 RX330 and anticipate using ski racks and/or a ski box on the factory racks. Looking at the Yakima web site, I see that you can attach a box or racks to the factory bars that run across the top of the car, or you can buy clamps to attach Yakima crossbars to the factory rails that run the length of the car. Does anyone know whether the latter approach is stronger or safer? Otherwise I don't see the point in going that route.
Thanks.