I have used a generator in rainy weather, although it is good to have some type of shelter over it.
I've seen five ways to deal with a CPAP issue fairly elegantly:
1: Some models of CPAPs have external batteries. With a charger, one can keep 3-4 batteries topped off, one in use, then switch them out with daily generator use for a couple hours.
2: As above, a "booster pack". These are definitely less expensive than external CPAP batteries, and should do the job. Only gotcha is that their power from the inverter is likely MSW... and some CPAPs may not like that.
3: A dedicated 300 watt PSW inverter (I like the Morningstar SureSine 300 watt inverter because you can place the inverter close to the batteries, then string 120VAC wire to where you want the outlet. Some outlets even have a 5 volt USB connection or two so it can charge tablets and smartphones. This way, you always have clean power to the CPAP, and coupled with a solar charging system, this should allow for prolonged trips without needing to fire up the generator constantly.
4: Bring along a UPS, and disable its buzzer. This can get expensive, since an online UPS can cost four digits.
5: Learning how to play the didgeridoo. Strangely enough, playing this seems to harden the mouth enough to stop sleep apnea. I'm sure this isn't realistic, but worth mentioning.
