Boondocking means 12 volt power supply.
This is not hard -- if your C-pap manufacturer can supply you with 12 volt adaptors for your machine.
My wife and I each use c-paps and we boondock. I use the humidifier and heated hose in winter. My wife doesn't use either.
First, check with your C-pap maker to see if they have a 12 volt power supply adaptor. I strongly recommend you get the 12 volt adaptors directly from the C-Pap manufacturer to make sure you get high quality and don't void any warranties. I ordered a 12 volt power supply for each machine directly from Resmed, who makes our C-paps. In the trailer I installed a 12 volt outlet (cigarette lighter style) on each side of the bed. I connected each to a 12 volt circuit that Grand Design had already (thoughtfully ;-) installed on one side of the bed for charging computers, phones and the like. My circuit goes back to the power converter and is 12 gauge wire. If you need to run your own wire, use 12 gauge which is sufficient for 2 machines. 12 volt DC needs heavy wire to avoid line voltage loss. You should be able to run it either directly to the battery or to the converter. MAKE SURE YOUR BATTERY IS REALLY A DEEP CYCLE. This is key. Otherwise the battery will not last long at all. Our two machines can run for at least 8 hours each night. Each morning I run the generator until the RV battery is recharged. No more than 2 hours.
My cost was about $100 for 8 feet of 12 gauge to go from one side of the bed to the other, marine style wiring connectors (the best kind), two 12 volt outlets, and two 12 volt adaptors from RESMED. It took me an afternoon to run the wire, make connections, test the voltage, and install the 12 volt power outlets. The 12 volt adaptors from RESMED were the most expensive, about $40.00 each. Plus the Generator of course.
Running the C-Paps off the power converter allows you to use the 12 volt adaptors if you are hooked up to regular power without pulling from the battery, and relying on the converter to sense that the battery is discharged and needs charging. It's worked for us for a year.