I have done Mammoth in the dead of winter. Mammoth RV has an indoor pool and hot spa, the showers are warm and the water is hot. The town is alive in the winter with plenty of places to eat or just hang out. Plenty of shopping also. The main roads are kept clear, remember, tourists are their only income. If you are prepared for 0 deg F at night you should be OK.
2014 Wind River 250RDSW
2014 Ram 2500 Diesel Laramie 4x4, Snugtop shell,
One big spoiled Bernese Mtn Dog