First: concerning towing in Park:
When I get hooked up, I put the key in position 1, place the transmission in neutral and pull the coupling knob. I then put the transmission in park. The key stays in the ignition.
At the end of the journey I place transmission in neutral and start the engine. You then simultaneously turn off the engine and mash the knob back in the home position.
I don't think MB takes a position on this. The service manager in Salem Oregon didn't predict dire consequences when I talked over my plans with him. His only warning was to use new bolts each time I disconnected the driveline if I wanted to tow that way.
Second concerning pintle style hitch:
The simple answer is I was only informed of the pintle style 20,000 tow bar. I was expecting to put on a 10,00 lb ball style, but the owner at Specialties RV refused to put anything less than 20,000 lb. I presume for fear that I would overload the van. I guess I could have done some more homework.
I issued a new blog on my personal web site today. There are several photos there.