I have been camping using my CPAP(Resmed S8 + Humidaire 3i) since 2008. I need the humidification and almost exclusively dry camp. My solution was 2 Group 27 batteries connected to a 300/600W pure sine wave inverter to power the CPAP. When we had a 5th wheel the batteries were stored under the bed. With the truck camper they fit nicely inside a "hamper" next to the bed. I connect the batteries to a charger/maintainer so they are fully charged for my next camping trip as the RV is parked next to the house and shore power plugged in. I can get four nights of sleep out of the two batteries without needing a recharge. If I camp longer, I use our Honda EU2000i generator plus a battery charger that I carry to recharge.
Yes I know that the CPAP can be powered directly from the batteries without an inverter, but you can't do that and use the humidifier.
And for you willy-nilly's out there, I provide adequate ventilation to the batteries when they are being charged.