I learned this on ambulance bodys, when I lived in Indy. Almost as bad as Mich. winter. Since u dont have a steel patch, try this. Like Pat said ddont grind metal down too thin, but u can also push the filler up behind the panel. Mix small amounts and get it in around the cancer, then fill the big area. If u need to put tape behind the hole till it sets up, and put filler behind after u take the tape off. I haave seen those amulances go for 5 yrs with a fix like that. Maybe u can find a good used quarter by then.