Originally Posted by porthole

I use one of these on our golf cart. Have the switch hidden.
This would work and is something to consider.

Use it between the starter terminal and cables.
It works with a magnetic latch, so there is no current drain other then when actually switching over.

Amazon.com: Blue Sea Systems 7700 ML-Series Remote Battery Switch with Manual Control (12v DC): Sports & Outdoors

Don't remember where I ordered mine from, but it was about $40 cheaper then the Amazon site.

This is what the switch looks like, but a momentary DPDT switch would probably work too.
Remote Control Contura Switch - PN 2145 - Blue Sea Systems