Be sure you understand the difference between an CONVERTER and INVERTER
A RV CONVERTER like the PD9260C requires 120VAC Shorepower INPUT and will then produce 13.6VDC OUTPUT.
An INVERTER like the AIMS Power 600W Pure Sine Wave Inverter PWRI60012S requires 12VDC BATTERY INPUT and then will produce 120VAC.
The CONVERTER and INVERTER model numbers listed above are just shown for examples... These are what I have installed in my OFF-ROAD POPUP trailer...
If it were me I would install one of these BLUE SEA 12VDC Plug and Socket Kit 1015 (AMAZON) close to where you want to plug-in your CPAP machine if it is capable of running from 12VDC... Otherwise you will have to install a 12VDC INVERTER that will produce 120VAC when you are not on SHOREPOWER. Buying the High Quality 12VDC socket and matching 12VDC PLUG insures a high performance 12VDC socket as compared to what you find at the local auto parts stores.
just me yapping
Roy Ken