Yakima Racks doesn't sanction the Yakima Kayak Stacker as being compatible with the 1999 Chevy Suburban roof rack crossbars. However, Thule Racks has the
Thule 830 Kayak Stacker that is recommended for use on your crossbars. And you don't need any extra adapters or anything. The 830 Kayak Stacker connects right to the crossbars. It does come with a pair of straps which will strap down the two kayaks on one side. But you will need to get another pair of Thule Straps to strap down the 3rd kayak on the other side (you can also add another kayak on that side if you ever want to carry four kayaks). The cross bar pads are not necessary but they do offer even more stability and help to keep the kayaks stationary in place. They also protect the sides of the kayaks.