2019, Nissan Frontier SV 4x4, Arctic Blue.
Just a general word of wisdom, you do not ever want use a neutral as a ground ever. It is meant to be there as a back up only, and combining the two creates a potential hazard for electric shock, should anything short out. That being said using a clean bare metal portion of the frame is not a bad idea, especially considering the wiring to go back to the engine ground would be a more complicated and unnecessary process.This is amazing and very helpful! I'm just about to start a very similar project but mount the battery in the truck bed. I may run an accessory wire from the bed (through brake light above the bed) into the back seats so i have the option of both fridge mounting options.... if i can find a good way to seal it.
one question, what did you do with ground from the aux battery? frame, starter battery neutral or onto the engine ground?