Here'a a portable 12v air compressor kit that was designed specifically for the off road 4x4 community so they can air up and air down their tires quickly. But before you click the link I just want to warn you that it is very expensive. It is a portable self contained unit that connects to your battery. It is high quality and you don't need ac power to run it. I don't have this kit but I have their on board twin air compressor mounted in the bed of my dually connected to a 5 gal air tank mounted under my bed. I have all the air I need for my tires and I can also run air tools if I break down on the side of the road...
http://store.arbusa.com/ARB-Twin-Hig...-P22666C9.aspx