I use a CPAP and tried a large jump start battery with 300 Watt inverter when dry camping 4 days last year. Left it at the Ranger station every morning and it didn't get enough charge to last the next 3 nights. So you need direct 12 volt. Most cpap devices will run 12v so order the cable from CPAP. Com or such. If you have a single 12v in your RV, suggest separate 35 amp deep cycle or convert to twin 6 volt like I am doing now. I was okay with just CPAP, but add a fan for cooling and it gets marginal. I also got a 100 Watt portable solar unit as I want to dry camp more.
2015 F350 XLT PSD CCSB SRW, Andersen Ultimate hitch
'12 Cougar High Country 299RKS, Mor/Ryde Pinbox
1/77 Armor Bn, 5th Mech, I Corps