I wanted to have an easy way to disconnect my house battery for servicing 12 volt appliances, etc., so I added a battery disconnect switch - accessible via my rear access hatch - Adding a Rear Hatch.
I purchased a switch, and a short battery cable:
Here are some shots of inside the battery box - it is tight, but it all fits (the small red wires and fuse are for the hitch lighting system, detailed in this article: Trailer Wiring):
Drilled a hole in the battery box, rerouted the positive cable (sealing the new hole I drilled for it), connected the short cable from the battery to the switch, and that was it!