"Normal" winters have daytime temps that average 65 or so in Yuma, yet there is always a possibility that it might get colder, or even snow in Phoenix. Phoenix does not get snow every winter, or even every 3-5 years, but it can snow there. Just a few miles away at a higher elevation of 5,000 feet, it does snow each winter, kinda nice to be able to ski there. Usually the valley is pretty warm around Phoenix.
Tucson is a higher elevation, and just to the east the mountains will always get some amount of snow each winter. Benson is around 3,500' elevation, if I remember right. You can click on maps.google.com and then Terrain, and search any area for elevations.
So avoid the higher elevations, and find someplace near sea level, such as Yuma for the coldest part of winter. Quartzsite is also warmer area, along with Brenda, they have a large RV park there, with many snowbirds who rent a place all year long, then store the RV on site for summer. Yearly rental is only about $1,200.
South Texas would be a great place to visit along the way to Arizona, and should also be warm. You can search
Weather.com and check monthly averages for any area of the country that you like.
Fred.
