I suspect those bolts will be chassis mounts. Not sure about the 110's, but these mounts may well be seat belt and body mounts to chassis all in one. Aluminium floor will be reacting with the chassis mounts. I'd be doing something about that ASAPTook the rear and 2nd row seats out, rubber matt out the rear, carpet up, guess what?
Very wet under the carpet, bit of hole and salts around some bolts, guess its the differing metals reacting.
Might have to look at all the door seals! And windows!