A "normal" primer is not going to prevent rusting. In fact, in some instances, it will actually promote surface rust. Like body filler, it is slightly porous to allow a top coat to bind to it.

That being said, if you are intending to media blast the area anyway then I'd "rattle can" the area with something along the lines of Rustoleum Rusty Metal primer.

https://www.rustoleum.com/product-catalog/consumer-brands/stops-rust/rusty-metal-primer-spray/

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