[quote|format=featured]***NOTE: This is a car trick, but it will work equally well here; supplies will be pricier.***[/quote]
Depending on how badly rusted the shielding is it may not be readily repairable. That said, if it's minor, you should be able to use the tricks @oldturkey03 mentioned or a [https://www.amazon.com/Rust-Oleum-Automotive-248658-10-25-Ounce-Reformer/dp/B003HG48AC|rust converter like this|new_window=true].
Once you convert the rust, you will need to paint over it. Depending on the area, cheap spray paint should be sufficient; don't spend $10 on cover paint when a $2 can of black spray paint is enough.
As far as paint and clearcoat, I'm going to lean on @oldturkey03 for that.