My main CPAP is a ResMed S10 Auto which requires 24V. To avoid the inverter / converter problem i shopped around and bought a used Phillips system one series 50. These require 12power up front so no inverting or converting. I also purchased the following:
1. $45 An ~100 Ah "Economy" Interstate deep cycle marine battery.
2. $45 A DC cord adapter set for the PR system one.
3. $265 A 100 A Renogy portable solar charger kit with travel case.
4. $150 PR M series 50 system one from CL
This set up while not cheap, was easy to set up and worked well for me while in the mountains this past summer. I really wanted to trim the costs down as much as possible but it was apparent that I would not be able to get by much cheaper doing it myself.
Using the instructions found here I was able to set the System one CPAP to my prescription and shut off all other power drawing functions. I also found instructions here for making a simple manometer for checking the pressure accuracy. Every thing checked out.
Pros of my solution:
1. Relatively cost effective
2. I have a 12 V CPAP back up for home emergency use.
3. I have a solar charger for the trailer battery
4. I have a substantial battery for cold weather jumping if needed.
1. The group 27 lead acid battery is heavy No backpacking.
2. The solar charger, while portable, is still a bit bulky and heavy.
3. the battery needs a bit of maintenance charge in the off season.
I still have to tweak wiring the trailer for the extra battery and add a extra rack for it on the tongue. All-in-all we are pleased with the way it worked for us (me).
Thanks for the advice