If you're going to go with a CO2 solution, I'd highly recommended having a compressor to go with it as backup. CO2 is absolutely awesome and ~8times faster than a compressor, but it can run out. Compressors are great, but can wear out and I find that mine will do 6 tires - plus or minus depending on ambient temperature - before the temp cutoff trips.
I have a compressor hard mounted under the hood near the battery, and a CO2 Powertank in the back. I've had to use both on the same run on a few occasions now, due to various unforeseen circumstances. As [MENTION=60147]the kid[/MENTION] mentioned, having an aux tank with the compressor is great for running air tools if need be, and the CO2 tank can do the same assuming you've got the juice.
If I were to do it over, I'd go to where I get my re-fills done and buy a refurbished and filled 10lb CO2 tank for ~$125 along with fill adapter and regulator assembly (pre-set or even the
Powertank model if you want to be able to adjust pressure between tires and air tools)and build my own rig for less than half the price I paid for the powertank.
Other than that, not much to know about CO2, other than the tank needs to be firmly mounted in your vehicle, and has to be upright when filling as to not let liquid CO2 to enter the regulator assembly.
A tip, at the end of your run, fill to ~4psi higher than your normal running pressure. You'll find that when your tires cool off, they will consistently be where you want them to be and you won't have to top them off later.
