I know this is an old thread but this is my cpap set up. First you need the 12v plug for it. Then I took a cheap Harbour Freight solar charger and mounted it to a battery box lid. Then got a 12v receptacle with USB ports. I wired a switch by the plug so I can turn it off and not waste battery running the red light. Then I measured from my bed to the ground and extended the wires that long. I set the battery under the bed on the ground and run the receptacle through the tent on my side. This keeps the battery shaded and dry. Then put the solar panel in the sun. Super easy and I have gone 4 nights this way. Don't know the limit. Only downside is carrying an extra battery.