It seems that the newer the CPAP machine, the more power it consumes, and in many cases, 12V becomes 24V. My old Resmed Plus CPAP consumed only 3A and has a humidifier. My new one consumes over 6A. My old one still works so I keep it on my MH for when I'm boon docking. I'm sure the newer one is better in some way but the old one seems fine.
So, if you have an older machine, check it out, but check with your doctor to make sure there's no medical reason to not use it.
2005 E350 Super Duty Ext Wheelchair Van
2002 Itasca 35U Motorhome