There are others that have much more experience that we do and I hope they will chime in but this is what we can contribute.
I fully agree with others that you should use the 15 amp electric to at least keep the batteries charged. Turn off the inverter and the breakers if you are concerned about pulling too many amps from the house but I think you run one 1500 watt electric heater with the charger in float mode. Remember the solar won't help when it snows. I also agree that the reflective insulation on the outside of the coach will be of minimal help. If you use your furnace the vulnerable bays should get plenty of heat to avoid freezing. Use the 200 W cube electric heaters on thermo cubes as back up or if you are going to use something other than your furnace for primary heat. As I recall the U270 has only one furnace but if it has two make sure you are using the furnace that heats the bays when the outside temps will be below freezing. On my U225 it was the front furnace. On my U300 the bays are heated by the rear furnace. Be aware that the generator may run out of fuel somewhere between 1/4 and 1/2 tank on the gauge. The tanks pickup for the generator fuel is higher than the engine fuel pick to make sure your generator will not run you out of fuel so the engine won't start.
I use 1/2" flexible foam inside the water bay doors, on both sides of the coach. Again not sure of your configuration but the added insulation should help prevent surprises. I use the reflective bubble wrap on the inside of the windshield, the rear living room window and the bedroom windows, the shower skylight, bathroom vent and kitchen vent. We have been below 10 degrees a number of times with no problems
Regarding dumping, when at my cabin I use a FloJet Waste pump, Amazon.com: Flojet 18555-000A, Portable RV Waste Pump, 12 Volt DC, Macerator,..., and a 100 foot, 3/4" heavy duty water hose to dump the tanks. If the house has a sewer cleanout within your 150 of your coach and you are on level ground you may not have to move the coach except for water.
Also if you need new house batteries, I used to buy 8D lead acid batteries from Sam's Club for under $200. From my experience, if your furnace is drawing down the batteries in just one night they may need to be replaced.
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