Shane:
I did my onboard air system in '98 when the Ram was new. It's been a swell deal to have plenty of air anytime. I run air horns, fill or empty my firestone bags, run tools, fill tires, etc.
I went to Grainger, the industrial supplier, and bought their best 12 v air compressor, a massively strong unit by Thomas. It makes the stuff at the Off Road Shops look 'discount' in comparison. It's the kind they put on ambulances, firetrucks and other Emergency vehicles. Back then, it was approx $ 500..... now, ??? ** But it's the most important item in your system, so why go cheap if you're going to the trouble to design & plumb the whole system ?
Next, a standard 5 gallon air tank from Home Depot, fab frame brackets to bolt to frame in space under bed passenger side at the front of bed, plenty of room. Compressor mounted above, with air switch and then connect the air line through inner bed.
I had a sheetmetal cover fabricated so when the bed is open, it's weather protected, and hidden. I then had it plumbed to the Air bag guage & control in the cab, mounted the solenoid for the air horn and also added quick disconnects at the tank itself for an airhose connection, and I carry a coiled hose to fill anything.
One improvement I'd like to make: I should take the time to have some braided steel air hoses made (maybe they're standard somewhere... . ) to help cure that slight air leak... .....
Hope this is of help to you... ... lots of good suggestions in the posts..... you won't be sorry once it's done..... makes your rig truly versatile.
It's kinda fun to see someone who desparately needs air lamenting their lack (usually it's a REAL need... ) and you shock the socks of of 'em when you click it on and air 'em up !
David B.
** The company that sold me the airhorns featured the exact Thomas unit in their catalog and it was $ 1300 +. I suspected such and the sales guy confirmed it was the same unit Grainger sold me for $ 500. He said they regularly sell them to municipal agencies, fire, police, etc and they don't complain about prices like us 'normal' folks do.
Lesson: I guess we give those guys so much in taxes, they don't have to shop around, right ?