I have a 2005 Fleetwood Pride 5th wheel with the arctic package. like yours, I have two switches, but mine is located in the front storage compartment. I only have one gray tank and the position of the switches may or may not be the same as yours.
I agree with Gordon in a previous reply to your question, that checking the amperage of each switch would be the easiest way to determine the switch for the two gray tanks. If your dump valves are like mine, they are located in the insulated underbelly and kept warm by the furnace duct.