Not sure about a Thule box, but noticing there is a photo in the gallery that features a cargo box:
Gallery | NiseRack.com
Based on that gallery photo, looks like a SportRack Skyline cargo box might be a possibility:
SportRack Skyline SR7095 Roof Box , Proline Truck, Car Custom Roof Racks...
Seeing all of that used to be in a day’s work. You need to take a load off by following one of your racks and making it out this way! Keep up the hard work—it’s much appreciated. Here’s another example of this great product:
