If you open the rear door and look down where the bumper meets the car there is a plastic strip that goes over the carpet rust forms under there but if the rear bumper is rusty more than likey so is the rear body.
On the 4 door models open the back doors to see if rust is forming in the corners where one body panel meets the other ( water just sits there )
There isnt too many area's that the rust but check all the normal spots eg-chassis just to make sure
Adam
