If you get any problem with the solder of 8 gauge wire on the controller PCB, may i suggest you something i did and that work really well?
I used some great home electrical box copper terminal for the negative ( due to the size and the proximity to the 4 shunt, it also help alot to dissipate the heat from the shunt and make it more stable regarding the shunt resistance value so the current limit will not decrease as the shunt try to heat up
It also allow putting bigger wire like 4 gauge if you wish too
For the positive i used a screw of the size of the hole of the pcb ( the thread of the screw just fitted perfect and tight
I used a screw that i can solder to the copper surface of the back of the pcb.
As you can see i also ysed big 3/16" diameter copper rod made for home electrical wiring ( 6 AWG) for the bus bar to help sharing the current to all mosfets.
Here it is!