Most switches will be a live disconnect on the positive. You don't need a fuse or breaker for this type of application and just a switch that disconnects the circuit, so you don't have to worry about amp or voltage ratings. Maybe someone else can chime in on that because I'm not an electrician. If you have two grounds I would place the switch on the positive. That will disconnect power and avoid any drains. All of my disconnects on my solar array, for instance, are on the live feeds. I use breakers on those though. Any generic 12v disconnect switch you find on Amazon would suffice. Just make sure all your terminals are clean.
Roads? Where we're going, we don't need ... roads.