The Thule 867 Tahoe roof bag is an excellent option for your 2002 Dodge Durango factory rack. Attaches directly to the factory rack bars. It's a great all-purpose cargo / luggage gear carrier and the whopping 17 cubic feet of cargo space for luggage and cargo gear offers a similar capacity to most more expensive (and not nearly as easy to install, remove & store) hard shell cargo boxes. Totally water resistant too, which is normally a problem with just about every other roof bag out there.
http://www.orsracksdirect.com/thule-867-tahoe-roof-bag.html