I think I would use #6 wire with 50a circuit breakers. The battery negative can go to the converter, then to the ground, or it can go to ground first. You might want to put a big fuse on the battery ground.
I wired my positive from the battery to a 150a disconnect switch, through a 50 amp circuit breaker, then to a copper buss made from a squished piece of copper tubing. The converter was wired directly to the copper buss, and another #6 wire came off the buss through another 50 amp circuit breaker to the fuse panel.
The first picture shows the general layout of the battery switch, and the Converter mounted vertically on the wall.
Second picture shows the battery switch panel removed to show the wiring to the circuit breakers, mounted above the converter. Red is positive, white is negative. On the wall to the rear you can see the connections for the ground wiring, including the green #8 chassis ground from the rear of the converter, and the lugs for the battery ground connection. All the lugs are tapped directly into a frame channel and coated in anti-oxidant paste.
The third photo shows a detail of the circuit breakers and copper connecting buss bar.