I took a look at the Yeti 150, that one would not work for your Cpap. It has a 14ah battery of which you would only have 7 amp hours of useable power. I think the average draw for the Cpap is around 3 amps @ 12 vdc. That would drain that battery in a matter of about 3 hours. The Yeti 400 would not work either, it has a 33ah (16 useable amp hours) battery.
You would be best off to get the 100watt folding solar panels c/w charge control from Ebay for under $200 dollars
2007 Surveyor SV230 - 200 Watts Solar/MPPT Controller - 230 AH Battery Bank - 600 watt PSW Inverter - (2) 2000 watt Inverter Generators - LED Lighting - Boon Docking 99% of the time.
2009 F150 - 5.4 Litre - 6 speed - Tow Package