Nice trailer! I think you did well. If it dips into the freezing zone at night, and warms up in the daytime, you should be alright as long as you keep the furnace and water heater lit. A protracted period of freezing temps could cause your waste tanks to start freezing, so you may want to put some RV anti-freeze in them. I don't know if it really makes a difference, but I put a gallon in each when empty. The theory is that it runs into the valve area pipes and everything else is added on top when used. Of course, useage dilutes the anti-freeze. maybe it's all psychological, but I feel better.
Anyway, we're headed to Indiana this weekend for one last three day trip, and I'll winterize when we get back. Right now, our trailer is sitting in the driveway with the heat and water heater on each night as the temps get down to about 30.
Have fun in WI! On our very first night camping in a brand new A/S, we were in Eminence, MO and it went down into the 20's. The furnace went out and would not re-light. It got cold! In the morning, i grabbed a hot shower to warm up. Felt good! My wife went next and quickly ran out of hot water - turned out the h/w heater wouldn't re-light either. She was frozen, and steamed too. We went to the A/S dealer in AR the next day. Turns out the power converter had failed and we simply ran out of 12v
juice. They put in a new one and we were good again. My wife reminds about that from time to time. I'd talked her into trying camping, and this was her first experience. She's really into it now, though, so I think I'm forgiven.