This stuff fills like no tomorrow, if you do use it be aware it is VERY transparent, you will run it if you try to get coverage right away, it's building way more than you think... slightly excessive in this case if you ask me, sand it as best you can with 180ish... epoxy and prime or use a good DTM primer and be done with it.... Rust Defender is a great product but has a huge build... in some cases excessive film build isn't really what you want.