Medicare will approve a new replacement CPAP machine every 5 years if a physician will authorize that you still need a CPAP machine at the 5 year points.
You might consider just getting a new CPAP machine. My new CPAP machine comes setup for use with a built-in humidifier that can be turned ON or OFF. However, I had to buy out of my own pocket a brick that allows plugging the machine directly into a 12V receptacle in the RV - so that no inverter is needed and thus using less power from RV batteries than through an inverter.
It will operate from 12 volts with or without it's humidifier being used. The brick cost about $90.