I use a CPAP as well and have a 12 volt plug
in system as well as a 110 volt which can be used in 220 v.
I installed a simple lighter plug
next to my bunk and it has been doing the job for over 4 years. If I'm doing a crossing I'll sometimes nap on my side without the machine but I have another plug close to my sea berth as well. I place the machine on the floor with some scoot guard under it.
I just replaced mine and I find the new one to very friendly on the use of power, using far less than my older one. If you use it without the humidifier it uses a lot less but I can't as it dries my throat out too much.