Some CPAP machines also can use a 12 volt connection. It is a separate cord that you have to buy if your machine supports it. My father bought this cord and rigged a 12 volt plug into the camper's battery and he carries an extra battery just for the c-pap when needed. What this does is allow you to run the cpap during the times when you can't run the generator. He has no problems with the battery lasting all night. During his testing, he found that one group 24 deep cycle battery was good for three nights before needing charged.
If I was setting this up, it might look something like this: (everyone has an opinion, right?) I would upgrade the batteries and have at least two, maybe even 6 volt batteries wired together to make 12 volts because of the extra reserve capacity. I would set up the cpap to run from a 12 volt source because it gives you more flexibility. Personally, if you have a 30 amp camper I would buy a Honda or a Yamaha 3000 watt invertor unit, or, if weight is an issue, two of the 2000 watt units and link them together. Others would tell you that the cheaper ones are "ok", and they might be, but this is a critical item for you, not something that is merely an inconvenience if it does not work, so I would get the best I could. As for the fires, that is usually the culprit of inexperience with how a fire works. Sometimes I even carry an already burning piece of wood to my neighbors and do some teaching about a smokeless fire.
Those are my thoughts, and may be what worth what you paid, but we have experience with camping with a cpap and that is what we did with good success. Good luck!
2000 Ford 4x4 Crewcab Dually 7.3 PSD
2015 Seismic 3712
2013 Jay Flight 32BHDS (sold)
2009 Jay Flight 31BHS (sold)
2005 Jay Flight 27BH (sold) - probably my favorite