positive battery cables

Those battery cables didn't corrode over night. Batteries need care and monitoring. I realize now the damage is done. You need a volt meter to start checking things out. Of course the negative cable should be RV chassis ground. Wire brush all the contacts. I would replace all the main cables if badly corroded. When working with battery cables I wrap red electrial tape on positive leads for future reference.

I would check battery water and for cable corrosion at least once a month. If the explosion box is wet inside remove the battery and clean it out and dry it before replacing the battery. Clean the corrosion off the cables. Take care of your batteries and they will take care of you.