Setting up RV to use water pump instead of Park Supply

I don't know of any automatic fill system for your fresh water tank. You will have to do what the rest of us do in that situation. Manually turn the valve to fill your tank and then shut if off when the tank is full.

I suppose you could add a soleniod valve to the inlet and rig a couple of sensors on the side of the fresh tank that would sense when the tank is full as well as when it needs to be filled. This would be more trouble than it's worth for me.