I have had onboard air in EVERY vehicle I own for the last 5 years. Needed my Samurai to get with the program. So, here is what I did:
I bought a pair of viair 400c compressors (one for my samurai and one for my Vitara). I have run 450c's in the last 4 vehicles I installed onborard air in; the compressors are very similar in size...the difference is that the 400c flows about double the air, but only has a 33% duty cycle. Perfect for filling tires.
I needed a tank...in the past I have always purchased an air tank from Harbor Freight, cut the handles and feet off, and welded mounting brackets and air fittings on as needed. In this case, I wanted the air tank under the hood and none of the HF tanks fit the bill. So, I decided to build one out of 6" sch 40 pipe. After calling some friends, I scored a killer deal. I traded some of my homebrew Blackberry Wheat beer for 16' of 304 stainless 6" sch 40 pipe. It is worth almost $1k new. I cut a 16" length of pipe, and TIG welded some ends on it, then drilled and tapped a 1/4" NPT fitting. I bought an assortment of air fittings from HF, and used my stash of electrical supplies from JC Whitney. I used a 6-bay fuse block and a self-resetting circuit breaker.
Here are a few pics of the final result: