As is my most terrible habit, I’ve done endless reading on this and am no closer to a solution (no matter how well informed I am - for better or worse). Can anyone suggest a solution for my particular application here?

I’m working on taking care of some rust that’s formed under the mounting points for my spoiler. The preference is to confine all of the touch-up to under the spoiler since the car is getting a respray in a year or so. It doesn’t have to be perfect. Sanding it all off down to bare metal was easy enough. There is some light pitting, and possibly some tightly adhered rust scale embedded in the pitting (not visible to the naked eye - the discoloration in the photo is residue from an iron digester I had laying around). So this is a direct-to-metal application with little rust, and I would strongly prefer to brush it on instead of spray. I do not want to use 2K products since it’s touch-up.

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I had previously purchased some high-solids rust inhibitor (rust bullet automotive) but they recommend a minimum of a 6 mil build and I know from experience sanding this shit is fucking impossible. I put a light-to-moderate coat on but it was flashing rust underneath within 2 days. So that’s gotta get sanded again.

I don’t want to do this three times, so what’s the best way to do it? I would think it’s etch/prime, fill/prime, seal(?), topcoat. Here’s what I’m looking at and considering.

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Eastwood self-etching primer - is this a good first step? Does the surface be treated with something to eliminate residual scale beforehand or will the etch take care of it? If so - rust converter? Fast etch?

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Step 2 - Rustoleum filler primer, or sandable primer, or primer surfacer? What’s the difference between these? I believe the filler/sandable are lacquer base and the surfacer is acrylic, and the filler is hi-build and the sandable is multicoat? I’m iffy about Rustoleum since their guidance is spotty- is there a better filler/sandable one-component out there?

Assuming I went with the Rustoleum sandable primer - does it need to be sealed if it is to be exposed to weather? And I assume primer/sealers are non-sanded sprays only?

Alternately - what have you used in touch-up, direct-to-metal work?