We were looking into a roof rack for a big camping trip this coming September, decided against it as we'll have plenty of room inside, plus the cost, but one thing I found, is that Sears sells a clone of the Thule boxes for quite a bit less money. We were looking for one that was on the shorter side, front to back, ideally to have both clearance for the tail gate and still be able to get some light in through the sunroof, and found one at the store itself that wasn't on line, that was I think around 15 cubic feet, and only 50-some odd inches long for less than $150, which is significantly less than the Thule boxes. The Sears boxes are just rebadged Thule ones. I do agree that if you don't mind not being able to open the tailgate with it attatched, a hitch mounted box might be a better way to go. I haven't actually seen one mounted, but it seems easier to get to, more out of the airflow, etc. Don't know about weight capacity, I think the Class III Draw-Tite has like a 300 lb tongue weight, which I think would be the max weight of your box, box mount, and all the stuff in it....