I don't get it, I have a group 34/78 in my 4 runner, it came out of my last vehicle. I also have an ARB fridge that I run in the back on road trips.
I left it on in the vehicle for 2 days straight, no starting the vehicle, no charging the battery, just constantly running the fridge at 30ºF. 2 days later, it started up without any hesitation. No sluggish starter, no dimming interior lights, nothing, just started up like normal.
I guess, if you have a grand to spend on doing a dual battery setup, more power to ya, but as far as I can tell, with an ARB fridge running all the time, unless you're gonna park somewhere and leave the vehicle with the fridge running for more than 24 hours (and setting it to 0ºF) without starting it up to charge it back up, its sort of a waste of money. Everything else you run, like a compressor or lots of lighting, can easily be done while running the engine, I know when I fill my 35's on my truck I keep the engine running the whole time while I do just to give the ViAir compressor plenty of juice to run for 30+minutes at a time.
Of course, this is all moot if you're using an electric cooler, as those will kill your battery overnight, since they run constantly and never shut off!