I put mine in the toe kick area right next to my power center.
Since my battery positive lead ran uninterrupted from the tongue to
the power center this made adding a cut off switch easy and I didn't even
need any extra wire. I just cut the positive lead and connected both ends
to either side of the switch. I'm just using a single battery switch.
Go to amazon.com and look for battery switch or harborfreight.com
or go into an Autozone and ask for a battery disconnect switch.
Many of us use this one. It's a little pricey but probably the best.