Follow all the ABYC requirements for this project.
The wire size must be selected based on the load current and the round trip length. When I do wiring projects, I bump up one or two sizes larger for extra power for the device. Here is a wire size table.
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
When I have added additional high current draw components to my boat, I have found appropriate alternatives to adding additional wires onto the battery terminals. The ABYC requirements limit the quantity of wires on battery terminals. It is common to observe a "rats nest" of wires on improperly "upgraded" boats.
The wiring diagram for this boat is in the linked document. Page 28 shows the MBSS feeds a power post on Page 28. That is the place I would investigate for connecting the high-current contactor and circuit protection for this device.
https://bbg1.my.salesforce.com/sfc/p/#E0000000Z21E/a/E00000000UNy/q5VMBLlC4ga2ZfS.wsfTpAvaw7KKARpm8MmqxZDTE6w
Don't forget to attain a secure installation. The usage of a thick backer plate, not just fender washers, will help to distribute the load for strength.
Don't neglect maintenance of this device, per the manufacturer's instructions. This is not a set and forget component.
