Very greenhorn @ RVing. Battery hook up question (pic)

From looking at your pic it appears that the black & white cables are used for jumpers between the two batteries.....so you can connect them white to negative (-) and black to positive (+) terminals on batteries

Then the cable on far right (kinda grey in pic) probably goes to trailer frame for ground
The cable on far left (red) probably goes to trailer for dc power

Just trace out which is ground cable.