I’m assuming you aren’t living in it, from our conversation last week. I would not rely on the AquaHot electric side alone. For the nights at least, if not for the entire cold snap, keep the diesel on also. The basement exchanger should keep up, coming on at 43F. The milkhouse heater is extra insurance as long as it isn’t a fire hazard and doesn’t blow a breaker, but may not be necessary. Leave a thermometer near the water bay manifold and check it regularly until you are confident your basement setup is working and safe.
Keep the water bay door shut tight. Check the coach before retiring for the night and a couple times during the day if practical. AquaHots can fail and power source circuits unexpectedly quit. The sub freezing threat is too great and the onboard systems too costly to risk not being vigilant for the interim.
The one place I’ve always been concerned about is the icemaker’s water solenoid valve behind my fridge. Son of a gun if this year I went to hook a hose to the coach for visiting family July 4th, and the valve was cracked and leaking heavily. It was easy enough to replace, but nevertheless I had dropped the ball somewhere over the last 3 years of “storage” and my disabling illness, not making sure the valve was drained, had antifreeze in it, or at least had 12 volts to the valve’s dedicated heat tape.
It looked like the latter was the real causation as the battery main switches may have been off during an extended cold spell. On the other hand the heat tape was out of position for some reason. No other (more expensive) coach component was affected. Obviously the hydronics wouldn’t have worked either without 12v. I thought I had antifreeze everywhere, but must’ve dewinterized and forgot during my illness somewhere along the line. I had dropped my usual vigilance, but got lucky that one cheap component was the only price. Usually my overkill winterizing includes both removing tube connections and draining the valve as well as cycling antifreeze through it.
So be aware of that one little but susceptible solenoid/valve. Being essentially outside the coach (right behind the fridge vented access door), it’s more exposed to the cold. There’s a trick to manually cycling the solenoid so it can either drain or accept antifreeze, and the valve isn’t even on many folks’ radar. If the heat tape is adequately attached around the solenoid, however, and the batteries are good and on, the tape should come on at around 40F automatically with no problem. Check it anyway.
Joel