As I said in my post, your simplest solution may be a battery pack made for your CPAP model. Your solutions are getting pretty complicated (OK if you need a new project ;-), and if you can arrange for AC charging during the day your problem is solved. Maybe the campground has a nearby store or gas station you can make a deal with. If you're in a National Forest campground, they can be pretty remote, so this suggestion may be useless to you. P.S. Fellow computer scientist and apnea sufferer.
