My view on onboard air I've debated long and hard on how to get an onboard air/air locker setup on the Xterra and after literally years of trying to figure out what to do I've decided the best bet is CO2.
Onboard air compressors just suck as far as output goes. And a cheap $300 air compressor setup is a lot more expensive way to fire a air locker than a $100 (at most) CO2 setup.
One of these days I'm going to get a picture of Hustler's CO2 ARB Air locker setup on the net for all 4-wheelers to see how much cleaner and cheaper a CO2 setup is.