As Vladis said, the jumpers on your batteries tying them together should be much heavier than the solar wiring
. You can get pigtails specifically for that at most auto parts
stores, even, for a few dollars each. Your Solar
controller wiring should go to the + of the one end of your bank, and Negative at the other, if I remember correctly. That's how mine is (same controller, but I have 2 batteries instead of 4).
When in doubt, fuse. I have it fused at the battery
just as you suggested, I figure that I might not HAVE to, but I'd rather be safer than sorrier.