MIke

I am not sure what you are asking so I will cover the big picture. A diode is essentially an electrical check valve. It only allows current to flow in one direction. So in this case when the towed vehicle is connected it would prevent the towed battery from trying to charge the coach.

I used this diode for my charge line, and it seems to be enough. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1