With my current rig I simply run a 600 watt pure sine inverter powering the whole rig at night. Runs my runs my S-9 Vpap through the night without any significant drain on the batteries even if I run the heater. The inverter is also powering our cell phone chargers, an alarm clock etc.
With our previous rig which we boondocked in almost exclusively without solar I had a separate group 24 battery running a 400 watt pure sine inverter that powered my machine. If we were only going to be camping 3 or 4 nights on long weekends which was our most common type camping I never bothered with charging the battery back up until we got back home. It would make it 4 nights before hitting the 50 percent SOC level most of the time.