Going to have a hitch assembly installed on my 2011 modified crew 144" HT. Having a 6000/600 lb towing capacity w/ 10K/1K lb weight-distributed capacity Class III Curt installed. The 20-ft Airstream is 4271 lbs with tongue wt of 631 lbs and GVWR of 5000 lbs. I do plan on having trailer brakes installed. Is this too much weight, though, for the V-6 engine or can the Sprinter actually do 7500 lbs since the factory-installed hitch through MB (at about > 3X the price) is rated for 7500/750 so it can do well over 5000 lbs by the looks - 50% more, in fact. We plan on using the cargo bay for bicycles and overflow of food, clothes, chairs that should not add up to more than 500 lbs. Thx for your thoughts and any experience in this area!