We have a similar setup like you, but we use a much larger aluminium plate to act as the heatsink. We also placed the esc inside a bulletproof ip 68 aluminium wiring box (it will handle a burning esc without trouble), and connected this with the aluminium plate by compression. We have also arranged the possibility to easily add a cooling pump if needed.
I talked to a friend of mine he told me that the if the esc is getting very hot, it might not be an ideal match between the motor/setup and esc, the heat is lost power due to bad efficiency. We got a new motor now (it says high efficiency…), will see if there are any improvements.
We use 10awg from the batteries to the esc and 12 awg through the mast, @pacificmeister do you use 8 and 10?