Dual battery set up and what to protect

I am in the finial stages of my SAS and complete rebuild of my 05 DCab. I am moving my battery and adding a second battery on the passenger side in the bed (inside my tool box). I will be using an IBS dual battery system to manage the batteries. the batteries will be optima yellow tops sitting side by side. I have ran the main positive from the engine bay back to the batteries using 1/0 cable and the ground are all tied into the frame.
eventually I plan to put all the OEM stuff and the winch on the primary battery and all the accessories on the second battery (mainly a fridge and a 1500 watt inverter)
my question is what do I need to protect with breakers? I will be using manually resetting breakers. I have been told I need to protect the main 1/0 cable doing up to the engine bay. I have also been told I only need to protect each 2AWG line coming from each battery before it gets to the IBS solenoid
So do I protect the line side(battery leads before the solenoid), the load side (main 1/0 Cable going to the engine bay), or both?