We have been staying in our 31FS for a couple of weeks now, while repairing our house. We have a small 750 watt electric heater. I thought it was a pretty weak electric heater on it's own. However, running it continuously helps a great deal to keep the RV temp more even. I can tell we use less propane when using the electric heater to help.
I also question the space this stay awhile fitting will take up in the cylinder bay. Hooking up a 20lb bottle would be very helpful, but yet more connections to ensure are tight and not leaking...