I use a ResMed S9 in my Outfitter camper, using the optional and not insurance covered 12 VDC #36970 power convertor. I had problems with it cutting out at night (due to low voltage) and thus have learned it is more reliable (especially in very cold weather) to not use the humidifier. (In these cases it was so cold in the camper I had ice/frost in the breathing tube, I also did not use the heated tube option) (Aside: I don't like to sleep with the heater "on" but the lowest the Outfitter thermostat can go is only 55 degrees so I usually shut the furnace completely "off" at night.) I never had problems using it in warmer weather.
I'd like to purchase a second machine (non-insurance, my insurance will only pay for the first one) dedicated to travel use and looking at Transcend or an HDMUSA Z1, neither of which I know very little about.
Not to hijack your thread but want to tell others I am physically fit, not overweight, and have never felt tired or sleepy during the day. Yet for many years I probably should've been on a CPAP machine. It was only because of an alert physician who during a routine visit, based upon heredity information and simply looking into my throat figured out I was a candidate for this therapy. An actual "sleep test" verified this. If you or your spouse snores at night please, please consider this.
My personal physician recommended I explore playing the Didgeridoo or bass trombone, (I used to play both, long ago), she (the physician) thinks it is good for strengthening throat muscles, to the benefit of fighting Sleep Apnea. I am game, but honestly both instruments aren't exactly what you'd call solo instruments (for practicing) and without a band to play with I don't know if I can commit to it. But another option I am willing to explore....