We towed our 2013 25FB International Serenity home through the mountains from Los Angles to Phoenix on I-10 using our October 2006 build 2007 Mercedes ML320 CDI with 4Matic, air ride suspension and a Hensley Arrow hitch.
I took the car from Phoenix to CanAm in London Ontario to have the factory installed receiver (was rewelded by a factory recall) reinforced. In the "Images" below my Avatar is a photo showing the 2"x2" steel bar reinforcement installed by CanAM. They also modified the straight Hensley stinger (goes between the female opening on the Hensley Arrow and the female opening of the car receiver) by cutting about five inches off of the car end bringing the trailer closer to the car as well as pre-bending it slightly downward to preload the weight distribution hitch.
It was not until January of 2007 that Mercedes wired the trailer brake system from the right rear to the front of the car. Thus we had to use the Tekonsha Prodigy RF brake controller which has an issue of pulsating brake application at the rate of the turn signals. There is no work around on my car for this issue.
The Airstream Literature tongue weight of 833 pounds was 1,150 pounds on my Shoreline scale at the dealership with the Hensley hitch head installed, the street and curb side awnings dealer installed, the factory installed 600 watt inverter and full water and propane tanks.
The 25FB with me in the car and empty crossed the CAT scales and the car axle weights were below the maximum numbers on the driver's door post. After loading the trailer for camping, full diesel fuel tank, the wife and and I in the car and some gear in rear of the car, the CAT scales reported overloaded car axles.
The trailer weighed about 6,960 pounds and the engine was not as happy pulling that load. The tongue weight after we had moved things around was 1,175 pounds camping ready.
We acquired a 2012 Dodge Ram 2500 HD Cummins and that solved all the towing issues. It is now towing our 2014 31' Classic. The Mercedes is now towing our 2015 23D and all the CAT scale numbers work out when camping ready.
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC
TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels