I'm not gonna tell people not to put a WDH on a Touareg - obviously lots of people have done it apparently with success. I just want to point out that there is a potential risk associated with it. And that VW is not just being obstinate when they say not to use one.
A tow hitch ball is what in structural engineering is called a pin or ball joint. It can transfer force (forward and back for pulling and stopping, up/down). It cannot transmit torques (rotational forces - trailer rotating relative to the car in both pitch and yaw, maybe a little roll).
The usual reason for designing with pin joints is that it makes the equations for static and dynamic equilibrium vastly easier to solve. Since torques aren't transmitted, the engineer only has to worry about the forces the trailer will impart on the tow vehicle. 3 variables instead of 6.
A WDH works by transmitting torques from the trailer to the tow vehicle. The tow bar system you've designed to be safe with 3 variables (the three torques being zero), is now encountering 6 variables. The results are unpredictable. It will
probably be safe - pin joint designs generally have to be beefier because they're not using the material's strength against torque. This results in the torque at a pin being converted into lateral forces, and your structural members have to be designed bigger to withstand those higher forces compared to a rigid design. But you could encounter a corner case where this isn't so, and the structure will fail due to being subjected to torques which it was never designed to withstand.
This is what caused the Kansas City walkway collapse in 1981. The construction crew couldn't get the walkways to line up right, so they converted what was supposed to be a straight cable supporting all walkways (only forces up/down along the length of the cable), into offset cables. That introduced a torque into a structural member which was never designed to withstand torque, causing it to fail and the walkway to collapse, killing 114 people.
https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse
The tow bar on the Touareg is simply bolted on with 8 bolts. When you use a WDH, the entirety of any torque they impart has to be transmitted through nothing but those bolts. It's like holding a baseball bat by only its very end, and trying to swing it. There's a greater chance that you're going to break your hand (bolt) or the end off the bat (frame the bolt screws into) compared to if you added a second hand further up the bat.
Again, I'm not saying A WDH won't work. Just that you're taking on an unknown risk by using one. If you're going to put a WDH and/or anti-sway system on a Treg, I would highly recommend considering models which add reinforcement structures attached directly to the vehicle frame, and not just to the tow bar. Or have a mechanic weld on a reinforcement bar from the hitch receiver to the car frame. That will help the hitch transmit torque to the frame, alleviating much of the torque-induced stress on the attachment bolts. It acts like putting a second hand further up the bat.
http://www.clubtouareg.com/forums/f...forums/f66/maxing-out-tow-capacity-with-travel-trailer-134082-6.html#post757681