First impression I saw was the CG, I looked up the website and the CG is at the 16' point of 21'. Now I don't know which direction thats from, but if its from the rear of the camper that puts the CG forward of the RA. Next question is where are the Fresh, Grey and Black water tanks located? It seems to me he would have had a full tank of fresh water, being in Mexico, I know I would have. Did he fill the fresh water tank after using some to the Grey and Black water tanks? If he didn't empty the near full Grey and Black tanks with a full fresh water tank, then its even more overloaded, then add on the motor scooter.
What was brought to our attention of frame welding, that was not in the initial article and is a big concern as I look at. My 04 2500 QC 4X4 needed 5ver rails to mount my hitch, due to the Hydro-Formed frame it was not recommended to drill or weld on the Hydro-Formed frame. I did a lot of research and found bolt on brackets to the frame that set the pin forward of the axle and the hitch fit perfect to the brackets. I had the dealer tell me its OK to weld on, and the RV installer told me its OK to drill on the frame. I'll bet the Camper Dealer just quickly welded on the supports not paying attention to locality or approved methods. I'm sure bolt on supports are available for that camper.
Big mistake was not to weigh it, but with the rear CG more likely behind the axle and welded supports combined is the probable cause.