I'm working on 2 additions this weekend - mounting the air compressor and installing a 2nd battery.
The air compressor is going on the driver's side, under the platform, in a little cubbyhole behind the wheelwell. I chose the driver's side because the bed floor has a bump-up relief for a fuel filler for those trucks with a second fuel tank. Since the space was partially obstructed, it made more sense for a permanent mount here, leaving the other side for storage.
Here, you can see the compressor, where it is going, and fitting it.