We use a cpap and Dw a Bipap, powering them from inside a rv is not difficult.
If the unit has a brick (large plastic box transformer) in the cord check the voltages on that. It likely is a 12 volt unit. If so, you can get 12 volt power cords to allow you to connect it to the trailers 12 battery power. My Respironics CPAP is listed as drawing a maximum of 5 amps at 12 volts, since I dont use the humidifier, it actually draws less than half that.
12 volt cords are available from most manufacturers for their models, you just need your model # .
If your unit will require 120VAC an inverter will be required to convert the 12 volt DC from the battery to 120 VAC, a pure sine wave inverter would be the safest for protecting the machine and will need to be more than 300 watt continious in size, preferably 500 watts.
Either way you will need a good battery/batteries on the RV with at least 40 amp/hrs available to maintain power for the unit, and a suitable method of recharging during the day.