"Warm Arizona" is a relative term... and not particularly accurate. From December through March just about anywhere in Arizona can experience severe {think mid twenties to mid teens}, over night. Keep in mind this is at the lower altitudes. The average elevation in the state of Arizona is north of 4,000' and if that is where you are the numbers get smaller with every foot of elevation gained.
Full winterization of your RV may not be essential in AZ but be prepared to take some preventative steps to avoid damage. We live at 3,400' a little north of Tucson and have seen 14 degrees, 4" of snow a couple of times a winter is not unusual and low temps in the 20's far from rare.
I don't flush the water lines but do open all the valves and drive around for a few miles to assist their draining completely. I then put RV antifreeze in the sink and shower traps along with half a gallon in the black and gray tanks. This has worked fine for the last 7 years and the coach is basically ready to roll 24/7. Just add water to the freshwater tank and roll out.
:C