This is why I hate (really hate) 12V systems for this amount of power, and hence current. The Blue Sea 6006 switches have a relatively high internal resistance. It’s why I don’t recommend their use for 12V systems. See a post I made here: PV 275A Isolator Switch dissasembly and comment - #9 by OGPS
If we are forced to install a 12/3000 inverter then we use two pairs of DC cables and two MEGA fuses. We use Blue Sea e-Series or HD switches with 12V systems.
In short, 40°C is acceptable given the way you have installed your system. Not great, but acceptable. If you want to reduce the resistance (which is causing your hot spots), then try the suggestions above. Good luck with your project.