More details to add to prior post.
The Mercedes dealer service chap in Scottsdale has always said our 2007 ML320 CDI was actually rated 5,000, pounds tailer weight. Andy at CanAm said the upgrade to 7,000 pounds was pencil whipped on newer models as no components were changed.
Our 2013 25FB International Serenity had a literature tongue weight of 833 pounds. The dealer installed street and rear awnings and a single 155 watt solar panel on the roof (could not recharge the batteries after a night of furnace use so a generator was necessary to top of the battery every day) and a factory 600 watt inverter was also installed. We put the Hensley Arrow hitch onto the trailer and with full fresh water tanks and full propane tanks, the tongue weight was 1,150 pounds.
I was alone with no stuff in the car when I drove the car and trailer at 55 mph to Phoenix from Los Angles and had no issues in the climb out of Palm Springs. The engine did end up in 5th gear at 2,200 rpm to maintain 55 on the steepest part of the climb.
Crossing the CAT scales when in Arizona after switching to the 15" Michelin LTX (P) 235/75R15 XL tires with Centramatic wheel balancers, all the axle ratings were within limits in that configuration.
However, after loading all our camping stuff into the trailer and a few items in the back of the car, my wife and I crossed the sales. This time the front axle ratings was exceeded and the rear was nearly maxed out. The trailer weighed about 6,860 pounds and the drive train was making new noises on very slight grades.
The Mercedes was retired from towing the trailer and replaced with our 2012 Dodge Ram 2500HD Cummins which now tows our 31' Classic with a ProPride hitch.
We acquired a 2015 23D International Serenity and fitted our old Hensley Arrow to it. Fully loaded for camping, some gear in the back of the 2007 Mercedes ML320 CDI and the wife and I in it, the scales numbers were not exceeded and the car has no issues even towing in the mountains. Towing at 55 mph, we sometimes see over 16 mpg on the flats depending on the number of starts and stops.
The Hensley Arrow stinger was also modified by CanAm in October 2012 when I drove to their location in London, Ontario from Phoenix (4,400 mile round trip driven in seven days with one day there) to have the (repaired due to a recall) factory receiver reinforced for weight distribution hitches. They cut about 5" off the stinger of the end that goes into the car receiver and slightly bent it downwards to help preload the weight distribution hitch.
Since I converted the 23D to the same 15" Michelin LTX (P) 235/75R15 XL tires, the elevation of both the 25FB and the 23D is the same and thus the same hitch settings were used. This rig drives like a dream.
My car was made in October of 2006 and it was not until January 2007 production that they actually connected the wires from the driver's foot well to the rear off the car for a brake system to be connected. Thus we had to use a Tekonsha Prodigy RF brake system. A permanent issue is that the turn signals will cause the applied brakes to pulsate at the same frequency the bulbs blink.
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