The number that will limit your towing is the payload rating of the Durango. Look at the loading sticker on the door frame. It will say "weight of passengers and cargo not to exceed xxxx lb". Cargo includes the tongue weight of the trailer, which is around 13% of LOADED (not dry) trailer weight. Tongue weight plus passengers and cargo in the Durango, plus 100 lb for the WD hitch cannot be more than the payload rating. You will exceed this limit long before you get to 7200 lb of trailer weight.
The Durango is a unibody SUV, meant as a people mover with the ability to haul a boat to the lake or a utility trailer to the lumberyard. A heavy, high-sided TT is going to strain its capabilities.
