Most CPAP's run on either 12v or 24v. Most OEM's sell the adapter you need to plug right into the 12v house battery. I use a portable Z1 APAP which I plug into the 12v outlet by my nightstand.
As for installing an inverter, I plan on doing that. It's really not too difficult.
Install there inverter in your front pass through or storage compartment using as large and short of a cable as you can hooking it directly to your battery through a fuse.
I have two outlets on my kitchen island, I intend to cut the connector between top and bottom on each outlet so that I can have two circuits, the top receptacle standard 120v and the bottom receptacle 120v inverter. I will run a cable from my inverter through the underbelly and up through the floor where the existing cables are going to the center island and connect the outlets.
I have a 200w portable solar panel which can easily top up my two T105 golf cart batteries.
I plan on installing either a 1k or 2k watt inverter with the 2k just to future proof the installation in the case I ever add 2 more batteries.
When I dry camp my biggest need is for my Keurig in the morning (yea, I know I wouldn't have to do any of this if I just perked coffee on the stove)
I found and purchased a 700w Keurig machine which does run easily on a 1kw inverter.
https://www.amazon.com/dp/B004978NKY...ing=UTF8&psc=1