Okay, simple. After my box flew forward, broke my rca cables and messed up the ground in my headunit (yeah, a common problem?) so now i have alternator whine, but thats fixed, anyways.....
You will need:
1) Good size eye hooks - something that will fit on your box, take a little beating, ya know.. a good size eye hook

2) about 3ft cable (yes cable, not wire)
Basically you drill holes in the box ( chose to not let it enter inside the box, afraid of air leaks, so I did it on the side. Find a good bolt and wrap the cable from the eye hook to the bolt and tighten down. Voila.
Yes, im aware im missing the big rubber price that goes on the metal