I used an inverter for years with my ResMed machine. Problem was that it was noisy and with the constantly running cooling fan it drew a lot of power.
Until I looked closely this past year I never realized that my machine was a 24 Volt unit and at home it ran through a 120V AC to 24V DC converter.
My supplier was able to sell me a 12V DC to 24V DC converter and it works great. It's absolutely silent and my draw on the camper battery is under a third of what I was drawing with the inverter.
I don't use my humidifier although I leave it in place set to off. The airflow over the water humidifies the water enough for me. Dave