We don't put RV antifreeze in water heaters because of the expense. If you are going to put it in there - you need to fully winterize.
The danger from freezing is when the water has no place to expand. It will expand and break things. An empty water heater tank with plenty of air surface can easily handle expansion of the small amount of water remaining in the tank.
Yes, RV antifreeze does turn slushy and will freeze if it gets cold enough - but it does not expand as it freezes.
Sanitizing - just wait until your normal pre-use sanitizing process - run the bleach/ sanitizing mixture through all water lines from your on-board water tank.
Rinse, repeat.
Personally, I don't put the anode back in until I'm ready to use the rig. Here in Texas I'm usually camping every month at some time between Sept and May.
We store our rigs in July and August, sometimes June - when it is too hot to camp even with 50Amp and two ACs running full time. The rig might be cool, but I don't go camping to sit locked in the rig.
