We are from Winnipeg and have left in October, November, December and January. Get a three day all clear forecast and you should be ok anytime. Cold the first day or two, but in most cases camping from then on. If you leave after early Nov. best to winterize the tanks and water lines.
We have travelled from Florida across and through to California, and to pick a spot for the winter the first time away is cheating yourself. There are great places with good weather and bad weather, no matter where you go. Your rig has wheels and they are meant to turn.
We still have not found the one place that has it all. (after 25 years of RVing)
Barry