You're going to have to figure out if you actually do have an inverter or not. If you do, how big is it (how many watts) and what outlets does it supply? Also, how many batteries do you have providing power to the inverter.
If you included the year, make, and model of your motorhome in your signature, people might be able to tell you what's normally included in that unit.
An alternative is to get a 12V power supply for your CPAP, and connect it directly to the 12V power in your motorhome. What model CPAP do you use?
If you were plugging your "outlet adapter" into one of the 12V plugs in the dash, those might be on the chassis battery system and only activated when the engine is running. You could install one of those (female) plugs on a 12V line in the bedroom, and use the adapter there. You'll need to find a line that's always active (before a switch), make sure it's sized appropriately for the load, and install a fuse when you put in the plug. Depending on the location of your batteries, it might be easier to run a new wire directly from the batteries to a suitable location in the bedroom. Again, make sure it's the right size wire and appropriately fused.
2008 King Aire 4562, Spartan K3(GT) w/ Cummins ISX, Motosat HD-SL5 w/ SWM-8, Multiswitch, HR34 Genie
2014 Jeep Grand Cherokee Overland 5.7L V8 Hemi w/ Blue Ox Aventa LX Tow Bar and baseplate, SMI Air Force One brake