l live in WI. I blow the lines out, and then pump antifreeze through sytem. Also make sure and take off all the fixtures like the shower head and kitchen sink head. Anti-freeze down the traps. Anti-freeze in the toilet. And I pour a gallon in the black tank because it lubricates the seals. You will have enough anti-freeze in the grey tank as you run it through the system. If you have interstate batteries keep a trickle charger on all winter if you keep them in the trailer. Many take them out. I don’t. Even if you take them out you still want to keep charger on them. I just keep them on the chargers. They won’t freeze.
About the coldest you will see in northern Wisconsin is -30. Rarely -40. I’ve lived in northern WI for 30 years. You will never see -50. And if you keep AS in a pole barn I wouldn’t even worry. You will be fine.
And by the way Eau Claire really isn’t northern WI. When you get up to Superior you are in Northern Wisconsin