In Canada every vehicle the GVWR and GAWR on the data plate mounted on the drivers door sill. My VW Jetta's GVWR is 1837 KG, front GAWR 985 KG, rear GAWR 871 KG. and it is also in the owners manual. Don't they do that the US? I suspect they don't show one for the Magnum on the website because they don't think most customers would buy a truck or SUV for heavy hauling but might want to know if their Magnum can tow their small TT, boat, ATV etc.
While Tow ratings and GCWR are not legal limits in BC, GVWR, axle and tire ratings are. Assuming 10% your 8000 lb trailer goes on the hitch and you put four people, pets and some luggage in the car, the Magmum would have to capable of at least a 1500 LB payload not to exceed it's GVWR.
Since the Magnum comes with low profile performance tires and not D or E rated HD tires, they might be very suspect as well. The Mercedes E rear suspension was definately not designed with heavy hauling as a major consideration.
The author makes some assumptions regarding the mechanical durability of the drivetrain. I was just reading a tech article in Mopar Action. Apparently the hemi's torque management system backs the power off during shifts to make life easier on the 8.3 inch Benz differential. Perhaps there really are some reasons behind these ratings that are quite obscure.
The author makes no mention of weighing each axle to verify that GVWR, GAWR or tire ratings were not exceeded. He may be advising people to do something that is illegal where I live, regardless of how good his opinions may be. He should make that clear in his article.