First,
to the forum.
From your description of the situation I would doubt that the regulator is bad and suspect the gas smell was from what you were doing.
I would fill the empty tank particularly since you are expecting cold weather and an RV can go through a considerable amount of propane when cold. Completely disconnect the hoses to the tanks. With both tanks full and the valves off connect the hoses to the regulator (note which tank the regulator points to). Make sure the hoses are connected properly (not cross threaded and tight). Open the valve on the tank that the regulator points to. The regulator should turn green, but, I've had them stay red until I actually turned on the stove to get gas flow (usually due to a lot of air in the lines). Once you have gas flow and a green indicator turn the valve on to the 2nd tank. Leave the stove on and SLOWLY turn the regulator arrow to the 2nd tank. It should remain green. Do not turn the knob on the regulator very quickly or you will have indicator issues. I think you will find things will work fine. As a note, I would always leave the 2nd tank valve on in cold weather so the system can switch tanks instead of running out of heat in the middle of the night and trying to make things start again. You don't need to know when a tank runs empty like that.....just look at the regulator regularly.
A regulator can go bad; and I've had one do it, but this sounds more like an operational error.
Hope this might help and you get it fixed.