Where the sills are the structural headline, the floors are where rust does its quiet work — often hidden under carpet and sound-deadening until it is well advanced. This is the second place to look after the sills.
Lift the carpets
The single most useful thing you can do is lift the carpets and mats. Damp underlay, flaking rust, or suspiciously fresh patches all tell a story. Soggy carpets are a classic warning sign — they point to rust in the floors below and, usually, to water getting in past a tired or ill-fitting hood. Wet carpet and floor rust travel together.
The floor pans and boot floor
Check the floor pans across their whole area, and the boot floor — a common rot spot. Look for the correct pressings and ribbing; replacement panels and past repairs can look subtly wrong. Probe suspect areas: sound metal rings, rotten metal doesn't.
The battery tray
The battery tray is a known corrosion point — spilt acid and trapped damp attack it over the years. Look for holes, heavy scaling, or a tray that has been patched or replaced.
What it means
Floor and boot rust is repairable and panels are available, but it is labour — and extensive floor rot usually travels with sill and structural rust. Wet floors also point back at the hood and its sealing. Judge the whole picture, not one patch.