Video: Installing a 600 Watt Pure Sine Inverter

Why not shorten up the 6 gauge wires and mount the inverter into the cabinet. Run from there with your 120v out and add a outlet or two or more throughout the camper where you need power? Even though you are not running big loads shortening the low voltage wires will improve efficiency.

I would also ditch those wing nuts on your battery terminal. They loosen with time. Or you could loctite them.