Breathe Deep...
I have done alot of high altitude XC's in the Bandit over the years including a Foray up to FL 200 once with a USAF 02 bottle and regulator(froze my butt off). Most of the time I stay at or below 12.5 for less than 30 minutes at a time where there is no requirement. However comma, after many USAF training trips in the altitude chamber to 35K unpressurized, I can assure you that even a small amount of 02 above 10K always helps, especially at night(vision).
I always thought 02 systems were too expensive especially refilling them with aviators breathing 02. Once, while filling my 02 tank for my welding rig, I asked the guy the difference between the 02 he sells for aviation, hospitals and my welder. He winked and said "not a dang thing" except price and label. I then proceeded to purchase a wheelchair 02 bottle at a yard sale for $15(much lighter weight too) with canula included and do some testing with my life support guys at my F16 unit. We filled the bottle with welders 02 and compared flow rates, 02 blood levels and quality with a USAF portable 02 bottle and regulator. No difference. I then rode along in the backseat on a buddies sailplane flight to 17K and tested it alongside a rocky mtn system. Absolutely identical blood 02 levels with the wheelchair bottle regulator set on "low flow". With all that said, I installed the wheelchair bottle on the back of my RV4 seat sideways with velcro straps. Works great, lasts 30 minutes at high flow, an hour at low flow with "aviator's breathing 02 in it"...
your mileage may vary...If all that seems too hard, Rocky mountain makes several wonderful systems...
Some tips on forays into thin air:
1. Have a blood 02 level sensor and know how to read it and use it.
2. Know hypoxia symptoms and act to correct them, now! Either increase your flow rate or descend...immediately.
3. Install the system where you can get to it fairly easily to remove to refill (easier and cheaper)I like the back of my seat, a bag of some sort riveted to the seat back would work too.
4. Get an altitude chamber ride if possible, excellent training.
Supplemental oxygen in an experimental airplane doesn't have to be expensive...
your call...
RR