I finally did my Dual Battery setup after a long time of putting it off. I did a very simple setup based off of @evldave on expeditionportal.com. I followed the following diagram:
I used an Optima D35 battery for the Auxiliary battery.
However, instead of just a regular isolator I opted for a Blue Sea 7610 that way there aren't any idiot switches being used that could be left on. This way it will simply charge and then if anything should happen it will cut off, leaving the main battery able to start.
So here are the items I used/purchased:
Off Grid 4x4 Battery Tray
Blue Sea 7610
Blue Sea ANL Fuse Block #5006
ANL 150 Amp Fuses
~10' of Red and Black 4AWG Wire
Connectors
I ended up returning the precut wire pictured. It was simple to just make my own small sections which I was originally worried about.
To connect the lugs to the ends of cut wire simply grab a dull chisel (or like thereof) and hammer the ends to crimp, the connection is fine.
While other write ups said it isn't necessary to use two fuses, I did to be on the safe side.
I also ran my Isolator into the dash so it starts up with ignition and grounded to where the main battery is grounded.
Here is my final setup
Finished in about 2.5 hours and right when the rain started.
Overall I'm happy with the outcome, glad it worked out and dont think I'm going to change anything major with this setup.