What paints for the heater box internals?

[In The Ten Ring]

I disassembled my heater box and have the metal parts in Evaporust. After just a few hours that metal was FREE of flash rust. So, what paint should I use to prevent their rusting in the future?

I normally hit small parts with NAPA Rust Treatment, then primer, then a top coat of black. Is that OK here?

I am afraid to drill out the rivet holding in the heater box flapper......my rubber around the flapper is intact and soft, but there is some surface rust on the metal part of the flapper. What do you guys suggest? What can that rivet be replaced with?