Well, you can go to http://www.thedieselstop.com
and do a search.
I found that the only place to mount my Bully horns was under the truck! Yep, I got a "marine" type battery box for the compressor, air tank and solenoid. This I mounted under the truck on the passenger side. I used existing holes and a couple of "L" shelf brackets to hold the box to the frame. Then I routed the air hose and wires across the frame member to the horns. The air line to the horns and the wires to the horn harness.
They have been there for 116,000 miles and six years of rain, snow and other road conditions. They still work and sound just as loud as they did when they were new. Just ask my wife when she is standing by her door and I hit the "panic button".
She still has a pretty good arm so I do it as far from her as possible.