I know this is an old post, but my buddy and I like to go off the grid for sometimes weeks at a time, and he uses a CPAP machine. Usually we just plug it into the vehicle's 12-volt socket for the night (with humidifier off). We've talked about getting one of those small pocket vehicle jump-starters in case the CPAP machine ever killed the vehicle's battery (so far so good). And we've also considered getting one of these Goal-Zero Yeti 400 portable power stations.
Seems like this Goal Zero power pack could come in handy for other things in the evening (like small LED lights and such). You could charge it during the day while driving (solar panel charging is also an option if parked for the day). I just think it is a cool product. I just haven't been able to justify the cost (yet). If you shop around you can get a deal on them.
And as someone else has mentioned, most parks and such have rules about quiet time after 2200 or so. And as a personal pet peeve, whether in an established park or not with rules, it is extremely rude to make other have to listen to your generator (stand-alone or as part of your RV) when out in the wilderness camping. I get away from it all to get away from it all, and that includes engine sounds running all night (and sound travels at night). Just because you're in an expensive RV and can't hear your generator running all night while you're inside it, it doesn't mean everyone else can't hear it outside. Nothing against RVs (sometimes wish I had one). And I don't care if the generator you purchase advertises itself as "whisper quiet" or whatever, trust me - it isn't. Oops - I'm getting myself all worked up - PTSD - must have had a bad camping/generator experience somewhere in the past - excuse me while I go think happy thoughts....