I found no information on winter use for your RV. There is no mention of cold weather use except for cautions about condensation.
http://winnebagoind.com/resources/ma...10/10Vista.pdf
Often insulated or heated compartments will be labeled as such. On my RV, the wet bay is labeled 'insulated and heated' and we have used it in below freezing conditions. The forced air furnace has a duct in the wet bay to keep things flowing. We have to keep this in mind when using space heaters, if the furnace doesn't run, the wet bay will get cold.
You might put a remote wireless thermometer in the tank area and monitor temperatures. An incandescent bulb or two can keep things above 32º if they are closed off and perhaps insulated.
You might contact Winnebago and see if they can tell you about cold weather use.