We had the Cheap Heat system added to our fiver and couldn't be happier with the choice. It works well down to 10 to 15 degrees or so and then starts getting a little behind where you will need to either turn on the fireplace heat or swap it over to propane. If you are paying by the night for a campsite (not metered), you will burn very little propane unless it gets below zero (yes we have been out at -5 F).
We also have the 2800 watt inverter with 4 batteries but would suggest upgrading to AGM instead of wet batteries. As noted above, they run just about everything except the cheap heat and AC systems. It is nice in one way as your satelite dish, TV, microwave and other electrical items will not need a long reboot time when you arrive as they remain on standby power the entire time.
For a longer run time with just the fridge running, turn off everything EXCEPT the fridge in the breaker panel that is dedicated to the inverter.
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