looking for rust on a z car = check everywhere....but primarily check floorpans,frame rails,under battery tray,around tail lights, wheel wells...when u check make sure to throughly check...like really poke or hit the pannels to see if its metal or bondo...u will be able to tell the difference...floorpans and rails can be harder to tell becuase of the undercoat...i honestly havent figured a good way to tell without removing some of it...