If it is like most lockers, it takes barely a sneeze at 90psi to activate them, and there is no "continuous flow" involved. ARB make a nice little mini locker compressor (not enough volume to pump tires etc), but would do the job well. Good thing is it is 5" x 6" x 3" in size and can run on a small battery if needed (only draws 5 amp when running).

I wouldn't go changing the earth to make room for powering the locker.

5 Gal tank will fill 1 or 2 tires from 15-30 psi, which means you still end up waiting for you compressor to do the remaining tires. Nowhere near enough capacity to run any air tools on its own, unless you are using an A/C compressor to fill it, even then you don't really need a tank anyway...(or as your mate does, a VERY high capacity compressor - >150 lpm/5 cu ft/min)

2002 Sporty , Ironman 2.5" spring, 2" body, 15 x 7 ROH wheels, K&N, 15 x 10.5 Simex Centipedes, Powerchip 91.

"Never argue with an idiot. They will bring you down to their level then beat you with experience!"