The wire size looks to be about 2 ga, I am planning on fusing the solar charge controller and inverter off the bus. the other wire will go to the trailer disconnect. There are a couple other wires on the battery's that I am going to move to the disconnect as well so all that's hooked to the batteries is a pos neg and trailer breakaway power. As for components the fuse will protect the 2 lines off the battery supply the whole trailer with 12 volt.
I'm trying to make room so in the fall when I gang 2 more deep cycles to the other battery's I have room for the cables plus with the extra 4 gauge wires for solar and inverter just checking the water level and getting the covers back on the box is a pain.