I added a tool box in the bed to mount my old compressor from a previous Chevy build and add a 2nd battery. I tried to use as least space as possible.
I plan to power all extra's from this 2nd battery (sound system, race radio, CB, lights, etc etc) and of course the compressor. I will run an 8G wire into the cab to a fuse panel to connect everything to. The compressor will go to the circuit breaker next to the 2nd battery.
I ran 1G wire from the main battery through a circuit breaker to a soliniod under the hood. The other end of the 1G cable goes to another circuit breaker then to the 2nd battery.
Just need a few more wires to finish everything as well as shorten the compressor cables and connect them. Also need to mount the under hood breaker and solenoid. The solenoid was going to be connected to a switch o I could turn it off or on to charge the 2nd battery but decided to wire it to ignition so it's always on. Only reason I used a solenoid and not a battery isolator was because I already had the PainLess Wiring 2nd battery kit with the solenoid and cables.
The box. Ordered from Amazon and it was not the one pictured but it will do the job.
Breaker installed 1G power & ground cable run plus an 8G cable:
I drilled a hole next to the battery in the box to run the cabling out and another hole just below the tie down hook in the bed and ran the cable though there, with a grommet Here's how it looks under the bed:
As it sits now:
Will clean everything up and finish wiring once I get a few short jumper cables.
I also bought a switch that will open and close with the lid. I plan on adding some LED lights to the inside of the lid for box lighting Just need to figure out how to mount them so they're aimed in the box.