i can confirm the thule cargo boxes, at least the ones with the click lok clamps, fit the factory crossbars just fine. Sits way the heck up if you have one of the flat bottom ones. If you don't I'd suggest buying one of the newer thule boxes that sits below the bars for mounting. All the newer thule boxes can fit bar spacing from 22"(min) to 26-33"(max) depending on the box size.
Wagoneer Measurements:
Distance from front to middle mounts - 29" center of bars
Distance from middle to rear mounts - 26" center of bars