Well, Ive been wanting to get a roof rack for some time. The fear is getting the sizing right. I just purchased a Chevy Venture Mini Van. It does not come with any roof adaptions. So Im thinking it might have to hook into under the doors/clamp down? Can I buy off the web, or should I go to a lbs and have it sized right. I hesitate to go through the lbs, I know the price with be very high, compared to going through - like Nashbar/