Stephen; I'm not trying to throw a wet blanket on the conversation, but if you get a hard freeze (below mid-20's) and lasting in the daylight hours you may be vulnerable. Heaters inside are not going to protect your water heater (which I presume is tankless) which just has a metal door with vents to the outside.
You may do a good job in protecting 90%, but you don't want a broken fitting to get you. Again I am talking about a hard freeze.
I blow out the lines (you need regulator on the air supply) and it takes 20 minutes. During the blow-out, each utility valve must be opened; hot and cold. Then dump a cup of anti freeze in each trap. Don't forget the toilet, shower, outside shower and washer (if you ever had water in that circuit).
You did not mention your motorhome type and when you are heading south.
Just more thoughts for you to consider.
Gale & Hank- 2012 Berkshire 390BH