I searched online and bought a 12v DC cord for each of my CPAPs. I also installed a 12V outlet near the head of the bed to avoid using a long extension cord from the 12v TV outlet. If you get a 12v extension cord, however, be sure to get a NOCO. Cheaper brands dropped too much voltage to power my inverter prior to my getting DC cords.
I tapped into the bed reading light for the 12v outlet, but plan to run wire from the battery and install one in the closet where I keep my CPAP to keep from having wire outside the closet. Besides, the DW hates it when the reading light flickers when the CPAP comes on.
To sum it up, a 300W inverter that plugs into a DC receptacle is quick and easy. A 12v DC power cord for your CPAP is a much better solution as it uses less battery than inverter/CPAP power adapter.