We live in New England and do not winterize as we use the coach all winter for winter sports.
Here and
here are posts with what we've done to protect the coach from freezing. The
2009 Dutch Star already has the basement insulation so you won't have to insulate them like I had to.
Last year we camped during the winter vacation week with record cold (-17 where we were). The supply pipe to the water pump froze but we were able to thaw it by turning the temperature up in the water compartment.
A new thing that happened is the fridge froze! Turns out that RV absorption refrigerators need to be kept above freezing, otherwise one of the pipes freezes. It stopped working until we got to warmer weather and it thawed out. Fortunately we had a nearby snowbank we could keep our frozen foods frozen in! Norcold actually has come out with a
Cold Weather kit which is essentially a heat tape you put around this pipe. Others have blocked off 2/3 of the vents and/or put a trouble light or other heat source on the fridge compartment.