We added a 2-way valve in front of the water pump on our Class C - the switched pump intake point was a tube that went into a gallon of antifreeze. We could winterize in about 15 minutes.
During our annual winter trip to Florida, we'd use a jug of water for teeth-brushing and cooking; and would flush the toilet with a splash of antifreeze. This would keep the RV winterized, until we got into an area far enough south to not have nighttime freezing temps.
I now use the jug-of-water system ALL the time for our stripped-down TC.