If the water is turned off, and no one there for several days, if if it were me, I drain the water heater and leave it turned off, if you feel certain the temps are getting below freezing.
Of course, the colder it gets, the less time it will take to freeze the water.
On several occasions, we've shut up our camper, but I've left a bowl of water on the floor for the dogs. I'd forget to dump the water. Even when temps don't appear to be too bad, when I go inside the camper, that bowl of water is frozen solid.
If it's cold enough, long enough, it will eventually penetrate everything and it will freeze. Besides, there's no guarantee that your furnace will run several days before running out of propane and you are not there. If you are running electric heat, you are definately going to have frozen pipes under the floor. The furnace must run in order to keep the underbelly warm. Electric heat inside the living area never reaches under the floor. It will freeze under there. Keep the furnace on. But failure can happen at any moment and you won't know about it, maybe for days. By then, things are frozen.
Best advise, dump the water heater.
About tank heaters. These are 12 volt DC and run off your battery. If you have a power outage and your batteries run down and you are gone, those tank heaters will not run any more.
When leaving the camper for a few day, always dump your tanks so there is nothing in them. You just never know when electric failure (both AC and DC) could happen.
Who you are right now is a sum total off all you use to be.
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually