Cheap dual battery setup, marine switch setup. Safe?

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Feb 2, 2016
Atlanta Ga
Hello all, I'm rigging up a quick simple dual battery setup primarily to run a fridge on my Atlanta to Alaska adventure. We leave tomorrow! So I'm down to the pun intended.

Anyway what I've got in question is whether the setup I'm working on is safe or if I need to rethink my plans.

I've got 2 batteries, each 1000CCA 115Ah lead acid.

What I'm proposing is running a 4 gauge wire from the positive terminal of the cranking (main) battery to a marine on off switch into the cab easily accessible i.e. The side of the center console or something if the sort, then another 4 gauge wire from the switch to the secondary positive terminal. Then simply ground the secondary battery to frame.

This will allow me to separate the main from the secondary when we turn off the truck for any significant period of time. Allowing the fridge to keep power flowing from the secondary battery.

The couple concerns I have is as such:

Do I pose any risk running such a long strand of 4 gauge wire that long length into the cab and to the battery, were talking several feet of wire?

Secondly, should I be ok supplying 2000CCA while starting the vehicle, or should I disconnect (switch to secondary on off position) every time I crank the truck?

Thoughts, ideas, concerns?

I do also have the option to leave the switch out of the equation and just run the batteries in parallel because the fridge is SUPPOSED to shut off if it detects low battery. But I don't completely trust this, I haven't been able to test it.
Any reason you don't use the 'excite' wire from the alt (or you could use the ign switched) to kick a heavy duty relay on so charging takes place but isn't connected to the vehicle battery when not running?

A simple switch (besides the runs of wire, and what gauge) is easily forgotten and potential to not be turned off...

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