hmmmm...so maybe I'll have to rent the auto transport instead of the tow dolly. That one at least has surge brakes on it.
To tow a trailer loaded with a 300D Merc with an HJ60, I'd recommend a class 5 hitch, load distribution hitch, tandem axle, trailer brakes and this would require at least one 24v-12v converter wired into your braking system so you can trigger trailer brakes and 24v bulbs in the trailer.
This package wont be cheap, Mark. Even with this package, most on this forum would consider the idea ludicrous. not me of course....
Anyway, my humble reccomendations...