The best way is to rewire the box useing a
30amp relay, 12ga. wire, and Deans connectors.
I posted a how-to on re-wireing a starterbox with
these features a while back. It is in the Off-Road
section of this site. Look for a thread titled "Ofna
Truggie Box". This way you don't draw a big amount
of amperage through the on-off switch or the bump
switch. Good luck.