I have been skiing since I was a little kid and still continue to 100+ days per year out here in Utah. During the summer months I use my mountain bike and hike/camp to stay in shape for the ski season. Let me know if you have any questions you can always give me a call 1800-409-4502 my extension is 4181 and I work Sun-Thursday 1:30pm-10:00pm
I called Thule and they said you absolutely need cross bars. I am sure you could jerry rig something up there but, Thule wouldn't endorse it or stand behind the warranty and security of the bag on top of the vehicle.