I use a 450 inverter for my cpap with heater tray. The heating tray takes a lot more power and is worth it to me . The inverter works a lot better if you can run it off its own battery
. By it's own battery
i mean dont plug the trailer in to the inverter and then plug your cpap machine in to a 110 outlet inside. ghosty loads in the trailer will shorten the battery time , with mine it would shut down on low voltage about 5 am and body say it needs at least 2 more hours of sleep .
I have found hooking a second Deep cycle battery into the trailers 7 pin connector and the plugging ithe inverter in to a 12 volt outlet inside and running only the cpap i can get a good 10 hour nap in. To recharge the whole thing i use a large 120 watt solar
rain and fog really slow the chargeing rate one of the reasons i went with a big solar
hope this helps