I've rotated tires twice now (per pattern in the manual) by jacking the front end onto my two jack stands and then placing the floor jack on the structural member between the rear wheels, where the differential would be on an old car. This gets all four wheels up at the same time. I see no damage on this center member, but am having second thoughts about using it. Should I be jacking each rear wheel separately at the indicated positions, or is it safe to use the center point and save a little time?