Thule cargo carrier?

I have a thule evolution cargo carrier on top of my jeep grand cherokee. Bought it 3 days ago and the weather has been very windy the last 2 days. We drove on a crosswind for 100 miles and the box moved. It's on very thight. Any ideas ?|||YES !!! As a fellow owner I strongly suggest you try finding a wind deflector, or "spoiler" to mount in front of the carrier.. Sorry, I don't know where my auto shop got mine, but I can say it made a BIG difference on my '07 Avalanche ! No more "roar, rumble or creep" 'cause the air's hitting the spoiler.....not the carrier.. Good luck..