12vdc Power Transfer Switch / Relay

[local343]

Hi there - Looking for some input on my 12v power/charging setup. My Daily Driver is not a yacht or even a motor boat, but after searching for some time, I hope someone here might be knowledgeable on this subject. Hopefully this will point others in the right direction as well.
I have2002 Silverado Truck with dual CS144 series 130 amp alternators, one battery bank (2-50Ah YellowTops), and isolated accessory/start battery. Batteries and alternators are currently isolated via Charles StartNow relay (which really only isolates batteries in dis-charge state).
Ultimate goal is to be able to run stereo and accessories down to low voltages and have no problems starting vehicle. I am trying to setup two completely separate circuits (battery bank being charged with future smart externally regulated alternator, and start battery/alternator powering all systems, including 150a max. stereo). Upon turning off vehicle, the power source would be switched from starting battery/alternator to aux. battery bank. I love the idea of having a 100% fully charged battery bank being charged in float at my disposal every time I turn of my truck.
All the transfer switches/relays I have come across are of the 120v/12v type (marine-shore application).
Is there such a thing as a 12v/12v transfer switch? I've thought about higher amperage relays, but this setup would involve dual inputs with common switchable output.
I like the idea of my truck running normally, and want to isolate the voltages that are sometimes associated with charging a depleted battery bank via external regulator from the normal operation of mytruck.
Brands I've been researching are Xantrex, Sterling, Balmar, Charles. Can anyone suggest others?
Any and all input-comments welcome. -Nathan