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Try using a derusting/iron phosphating chemical like chemtex or Captain Lee's rust away.
They'll remove the rust and leave behind a grey iron phosphate coating that is mildly corrosion resistant (also an ideal surface for repainting or powdercoating).
Any decent automotive paint shop will have products for this type of application. POR-15 is a good product that I get at my paint shop.
Eastwood has a product called After Blast that leaves a zinc phosphate coating, that's even better at preventing future rust formation. That would be an excellent follow up to navel jelly.

Never, ever, using Muriatic or any form of hydrochloric acid to remove rust. Yes, it does so quickly and at first glance efficiently, but it leaves behind Cl ions that bond to the steel and merrily kick out out carbon molecules to be replaced by oxygen molecules and the rust goes on and on and on...(it's the Cl in NaCl (roadsalt) that makes cars disappear).