A tow dolly is also hard on the steering.. you my find powersteering fluid puked out onto your shiny engine if you have many turns on your route, but you probably have a flaming river so OP should be good there. Also can't back a dolly up effectively, so you always have to leave yourself an exit. It can suck if you take a wrong turn. Also, along with the near zero tongue weight, when taking sharp turns on gravel (like navigating a tight dirt lot packed with semi's) the car and dolly will want to push the rear into a jackknife when trying to stop with surge brakes. There is thousands of pounds of rolling force trying to push your rig sideways in the dirt on the ball on the very rear of the vehicle. Maybe more stable on a 5th. But as far as that, put a good cover on it, whatever your tires kick up on the road will be flung toward the Merc.
Sure you don't want an enclosed trailer and a rented truck?
Sorry, I know nothing when it comes to 5th gens. Can't help there.