bases up works best in open ski racks, sometimes you can't fit all the skis like that, in that case, especially with ridiculous rockered skis (Caylor, Hellbent, Pontoon, EP pro, etc etc) it can be best tie the tails (front of car) together with a ski strap or cord or whatever to keep them from flapping around. If you can securing a bag over the tails and tips will help your gas milage, and keep the skis cleaner.