How do I wire trailer winch/battery to truck batteries?

[ChrisKringle]

I have 10000lb winch on the front of my 16' flatbed trailer for getting my broken jeep on or pulling off a load of debris (pulley welded to rear, and small sled at front) off. I currently have a full size auto battery on the front of the trailer that will run the winch throughout the day, then trickle charge it at night.

Now, here's what I want to do and bought parts for today. Run a heavy gauge (friend got me 1/0) cable from the batteries positive lead all the way back to the bumper where I will drill it for a flush mount female welding cable recepticle, then on the trailer have a similar heavy gauge cable run from the positive of the trailer battery/winch to a male welding twist lock connector that will twist into the aformentioned flush mount female recepticle. The reason for this is so I can have 3 batteries in parallel for all the current I will need, plus the trailer battery will charge when the vehicle is running. Oh, forgot to mention the 200 amp mechanical inline relay that will only allow the trailer battery to be connected when the vehicle is running.

Everything sounds good to me, but here is my question: What about ground? I was thinking about connecting a heavy ground strap from the battery negative to the trailer frame, and just let the current run throught the trailer tongue/ball intersection and ballmount/truck receiver intersection. The ball/coupler union of the truck/trailer looks clean, no dirt, and I dont use grease, I dont see how this could not work, will it? I use the aluminum adjustable dual ball mount. It will save me running another ground cable from the truck frame to the trailer frame via welding cable and quick twist connect.