These are desperate conditions indeed. The lowest temps. I had my 1978 Vogue diesel in was -20F ambient temperatures in the late '80s way Up north, before I recall the pink RV antifreeze was even marketed. I drained the water heater and the water lines, as well as unscrewing the water pump hose line. I don't recall having any trouble when I re-plumbed it, so maybe I was just lucky.
I broke down and did the RV antifreeze formula last week instead of running an electric floor space heater night after night when the coach is in my driveway. It's not often air temps get below +15F here in North Texas, so I guess I'll be OK.
One thought - if I had to prepare for the -30F temperatures, and only had RV antifreeze, I would flood the plumbing with the RV antifreeze formulation fully, then open up all the floor drains and unscrew the intake hose from the water pump too. This would not trap the RV antifreeze at those extreme temps - it would be less likely for any RV antifreeze remaining in the system to have enough quantity to expand, rupturing or bursting any plumbing hoses.