Thanks to all of you who have responded to my plea. I am not surprised that this is more complex than I had (naively) hoped so I need to do some reading. For now, we are going to see how far we get on our batteries and go from there. I will call the cpap manufacturer (Resmed S9) and we might consider getting some sort of power pack for the cpap itself.
Will report back. Again, thanks.
Kathleen and the "Big Guy" (BG)
Homer the Beagle
2016 Acura MDX - 2015 X20E
10K Equalizer; Teshonka P3
Dual 6V Deep Cycle Interstate Batteries