Les,
The engine starter motor on a C-12 can have a momentary draw of 500 amps, so I would not use any disconnect switch that is rated below 300 amps continuous duty and 500 amps momentary duty. A higher rated switch is even better, but I would consider these to be minimum ratings.
The switch that Tim posted a link to on Amazon would work for house batteries, however I would use a heavier built switch for the chassis batteries. The switch that Gil posted a link to will handle more amps than your starter can ever draw.
Gerald