Boondocking & CPAP.
Yes, run the CPAP & or humidifier directly from any 12 volt outlet directly, no inverter, when shore power is not available.
I would also suggest a small generator or 100 watt minimum solar install to keep the batteries charged & not let them get below 50% SOC.
Check your converter & determine if it has a 3-4 stage built in charging system. I doubt it does, but that would be beneficial to maintaining a good charging profile for the batteries in conjunction with shore power or the generator
I personally run my CPAP from a dedicated 35amp 12 volt AGM battery, so not to use the coach 12 volt system, recharging it as needed.