Why do they use 8 AWG cables, pain in the a** to solder. 10 AWG is enough.
Ace hardware stores sell an 80 watt soldering iron with a 3/8" chisel tip for around 30 bucks. I t will make all your large soldering jobs a breeze. The key is not the watts but the big fat tip, it holds all the heat than dumps it all on your part in an instant. A smaller tip will just slowly transfer heat to what you are trying to solder and never get the joint itself hot enough. I used the tool for soldering battery bars an 2600mah A1213 cells and it worked great. I was able to tin the cells with globs of solder and the tool was on and off the cell in less than a second, with no heat transfer to the cell. I wouldn't think of using anything else but that for #8 wire.