Well, first, YOU DO NOT NEED TO GET AN INVERTER for a Sleep Apena machine.
You need to get a machine that is capable of being run on automotive battery power.. Way less expensive than an ivnerter (Bascially same price as one that needs 120 volt so the difference is free or 5 bucks for th 2nd power cord)
Then you run heavy 12 volt lines to the bedroom. (10 amp at least, common 12 acc outlets are rated 10 amps, HD ones 20).
Personally I like better connectors but those need technicial skills to install which many dealers are lacking.
Option two, Google 300 watt true sine wave inverter
most all of 'em are good, Inverter goes near (but not in same air space) as battery and run an extension cord to the bedroom.