Leyland Car Owners - Rear wheel arch rust

While removing the rear bumper to ready the rear left quarter for repair, I noticed so flakes of rust on the left hand turret raise floor.
: With the aid of the screw driver, I did some poking and found that the blade pasted through the car body into the wheel well.
: What I found is that after they had assembled the car, the metal work in the wheel well was not treated or sealed or they must have run out of the sound deadener.
: What they created was a cavity where dirt and water was able to enter and sit. A rust pocket
: I would suggest an inspection of the boot as well as in the wheel arch for signs of rust.
: What I need to do is to try and remove the flakes of metal, dirt and rust.
: Treat the rust surface with a converter, then fill in the holes with gorilla hair bog.
: Apply new sound deadener again in the wheel arch.
: Cheers Adrian

Rear wheel arch rust