I'm not in WA, so I can't take the job, but I can make one recommendation about that wiring to the tub.
Use 60A cabling, send both positive and negative down together, and the best way is to use double-insulated stuff, because of the extra cable protection and ease of installation.
Don't rely on the chassis earth. Connect both wires directly to the battery, install a 30A thermal-reset breaker as close to the battery as you can manage and if you're passing through any metal walls, use grommets to protect from chafing, because over time, the cable WILL move and it WILL wear through the insulators causing a failure, and it will probably happen right when you need it most.
Any good electrician will probably tell you the same - but just in case, you now know what to insist on.
Enter your email address to join: