BarryG

I have an 01 so it may different but on the pass side directly behind the cab under the bed I took four pieces of 1" square tubing with the holes already in it got it at home depot. Mounted the compressor to two of the pieces then took the other two and put them on the inside of the frame rail then bolted those inner and outer pieces together sandwiching the frame between them. With the holes in the tubing I was able to raise the compressor side as high as it would fit up underneath the bed. I then took some diamond plate aluminum I had laying around and made a box for the compressor ( I left the top open for air flow, cooling, air and electrical lines etc) I was also able to use the holes in the tubing to mount the plate to. It has been there well over ten years and no problems. I mounted my tank using the rear under bed cross brace using the same technique except I did not have to use the tubing on the underside as the tank was long enough to not need it. In the end it is very much protected and if you look you will find very little gunk gets up that high and my air filter I can still get to because of the open top box without taking it all apart.

Asher

I think I found the only usable free space on the truck that was hidden away. I made a couple small brackets and mounted my Viair 444c inside passenger fender and the air tank inside the drivers side fender. It's a tight fit, but everything is out of the way, hidden, protected, and took up no space in the engine compartment. I don't have many pictures of it, but these might give you an idea... This is the drivers side tank mounted, the compressor is pretty much a mirror image..

Mexstan

My original mounting was behind the LH rear passenger seat. The valves went into the storage area below the seat, but between the upholstery and the metal side of the storage area. The compressor had to be mounted on it's side which I did not really like, nor is it recommended by Viar. It was attached to the back of the cab. Worked fine but oh boy, was it noisy!!!!!

I have now removed everything and the whole lot is now mounted on a floating base in the toolbox in the bed of the truck. Now also run two Viar 350C compressors in parallel. Cannot hear them now with Cummins running. Mounted a very small LED (just like the A/C light) next to the compressor switch on the dash so that I know when they are running.

GASKICKER

This is probably the way I will go too, looks clean and protected.
Did you happen to take any pictures of the compressor mounting?