Today I finished a rust repair on 2006 Corolla on a section about the size of your fist. That was due to some old bad body work where the paint had cracked. Rust and filler, I suspect they just dimpled the steel and filled with Bondo. After chipping out the old paint there was rust underneath, used a wire wheel on the cordless drill to get rid of scale. Then painted with 4-5 coats of Corroseal rust neutralizer followed by 4 coats of Dupli-Color 2-in-1 primer filler that try as I might, could not fill the wound to quite the same height as original paint. I masked it to about 6” square area for the primed area, then used Dupli-Color color matched paint which looks OK for AutoZone aerosal cans. The body shop paint was very weathered and chalky so I had to paint a lot more. Then spray clearcoat. Frankly it looks like a repair the car owner did it but it’s respectable looking of what was quite an eyesore. The main objective was to repair the rust and make sure it won’t rust through.