If u can find Duraglas body filler, there are some other brands, grind the paint and loose rust , and fill it all in. With the waterproof filler it will never rust out in that spot again. Only use bondo type as thin layer over Duraglas type fillers. And put the Duraglas on in thin layers until u get used to working it as it is really strong and can be tuff to sand if u get too much hard filler at one time.