There is ALWAYS a chance of extreme weather here in SW Ohio. ( I have photographs of snow on flowering Redbud trees in late April. ) As long as you can plug in I have dewinterized in early April, even late March. If there is a cold snap just plug in an electric space heater and open the cabinet doors under the sink(s). That has even helped me through a few days gap between trips in mid winter when I didn't want to winterize, then dewinterize a few days later.
Finally, if you are traveling in cold weather you can still use the toilet. Keep the camper winterized and carry a large water jug/dispenser. Just add some to the toilet. Flush (with the water pump off so you don't pump in anti-freeze) and replace the bowl water. A touch of antifreeze in the tank usually isn't needed but may be wise if it is really cold.
