Connecting Marine Battery in Popup
So we purchased a reconditioned marine battery for our '94 Jayco 1006 pup, which I'm learning should be fine as we just need it for backup since we'll be camping at CGs with shore power. But after dropping the battery in the box, I have questions on hooking it up. As pictured, there is a plastic white connection piece hanging off of the black wire that (I assume) is the live wire to power the units in the pup. I know that the white wire is the ground and connects to the negative (-) post. Is this white thing a fuse container? If so, what size fuse should I use? How do I connect the rest of the black wire back to the battery (+) post? Help is appreciated, yes I'm new to all this so bear with me, thanks!