You certainly can build a 2003 Ford Explorer Sport Trac roofrack system to accommodate the
Thule 897XT Hullavator kayak rack and the
Thule 830 Stacker kayak rack. I highly recommend choosing the
Thule 450 CrossRoad roof rack base system which connect directly to your Ford Explorer Sport Trac factory roof rack side rails. This system includes 4 Thule 450 Crossroad Feet that attach to your siderails, and 2 Thule load bars that connect to the 450 Feet. The 450 converts your factory rack into a sturdy base rack system capable of safely transporting your kayaks. You can then connect the Thule 830 Stacker and the 897XT Hullavator to the base rack load bars. Just be sure to choose the 65 inch load bars to provide the room necessary for this set up.