Another issue for Cheap Heat is that they can't be used at all with a 15 amp service. Whereas a stand alone heater can still be used to dramatically reduce propane consumption.
It is easy to add an additional auxiliary shore power cord. In my case I added two, so I can use the OEM 30, a 20, and a 15 amp. That means, if there are sufficient 15 amp circuits, I can have up to 5400 watts of heating available. Of that, I never use more than 1440 per circuit (80% continuous load).
The OP's question was about preventing basement freeze up. On a 30 amp service the Cheap Heat would prevent such a situation. But so will a $25.00 dual window fan. It is currently -3 c (26 f) where I am. It is taking 2500 watts to keep the RV at a toasty 21.5 c (71 f). That would mean having the 50 amp version of the Cheap Heat. The 30 amp version would not be adequate to the need.
My peak load in the coldest part of winter is about 7100 watts. Which means that even the Cheap Heat 5000 watt would be over matched.
I do realize that many folks don't camp in weather at extreme low temperatures. My best "guess" is the Cheap Heat 5000 watt can manage down to about -20 c (-4 f). After that--you will burn a LOT of propane. My own experience is about 100 lbs in 72 hours.