We have used the Thule 830 Stacker on our jeep grand cherokee with factory roof rack for about 6 years. They work great for our two Necky 13 footer manitous. Reasonable price, good solid rack, and work well. Hefting the boats on top and then strapping them down is a bit of a reach but we have done this for quite a long time. At first we used straps on bow and aft as well as to the car top racks, but now we do not as they ride very secure with no slippage. But--If I had a high dollar boat with a fine finish on the hull, I would not want to subject them to the strapping and direct contact with the stacker and car rack cross bars. But for our very usable boats they have been just fine. Enjoy the boats. Jim