Tales from the dark (dead battery) side.
The test run above goes to show that there is no way to do the math to come up with the "ideal" set up.
In the test, the frige was set at "it's coldest setting". If there wasn't anything to freeze inside the frige, it probably tried to kill it's self by over cycling. There are so many variables, you can only do your best to plan for the worst.
For single night campers, yes, a solar panel would be a waste of money. But a second, isolated, deep cycle battery is never over kill.
The condition of your starting battery will change ever so slightly every time it is used. By adding a slow constant draw to the starting battery that will drain it below it's normal voltage range is a recipe for disaster. If you are mainly an over night camper, the piece of mind knowing that you have a completely separate secondary electrical system is well worth the investment.
When I was towing with my Tacoma, I had my ARB in the back seat set on the medium shut off setting. My ARB set on medium shuts off @ 11.2 volts. The Tacoma needs 11.3 volts just to operate the fuel pump for the injection. Stuck and I was pissed. That was the last time I only had one battery.
With my 100 series, this will be one of the first changes I will be making and then I link the second car battery to the trailer battery so I will have combined 200 AH of storage. There is no reason to use large cable/wire like 6 ga. because you will never have a large amp draw in this system. But if you have the cable, run it. I have a 200 watt inverter in the trailer and it's sets right at the battery with nice short fat cables.
Just a tale from my experience, it may not be worth .02.
Jeff:beer: