I read all info on Sprinters structure I can get and we have paralel topic, where I applied some pictures.
Sprinters vans are build as unibody with not much framing design for holding weight in the rear. No crumpling zones makes the main shell taking any impact and several pictures show that rear impact makes Sprinter folding over rear axle.
During my conversion I experienced that Sprinter body is all build from very mild steel. Wood cutter cut right thru it, while decking screw will go without predriling.
So my conclusion is that even 500lb on rear hitch is a stretch for the design.
Than ClassC are build on extended body, who has even more stress, but built as cab & Chassis they have frame, so something to investigate.
I have not seen Sprinter C&C, but had motorhome who even in Class A were build on 28' frame extended to 32' as the converter wanted to maximize the profit. Is Sprinter ClassC having frame extended beyond common sense?
OP did not say what exactly he is going to pull.
I think 5500lb boat with 200 lb tongue weight would be acceptable risk, but 6000lb garbage hauler with 800 lb tongue >>> forgatabouit.