I would simply treat the freshly media blasted pieces/parts with a phosporic based acid product, like Picklex 20, then either use a 2 k Epoxy Primer, or Rustoleum rusty metal primer, use the rusty metal primer either in aerosol format, or use the canned stuff reduced up to 40% with automotive enamel reducer, then spray on with paint gun using a 1.3 to 1.5 tip, a cheapo HVLP gravity feed gun work well for this.
As the said parts will be in storage indoors, the Rustoleum needs to fully cure about 2 weeks, then any enamel or Urethane paint can go over with no issues.If you go with epoxy, just check the re-coat windows, but it will need a scuff after a short period.
If these are small panels, ie exterior panles, the same can be done, just keep in mind if using Rustoleum primer, to give this a long period to fully cure, after this, anything goes, 2 k urethane primer, lacquer based primers, epoxy primers, auto body fillers, etc.
Do not use any acid etching primer over the above mentioned products, acid etch primer is to be used only on bare steel, then I would go over this with epoxy primer, read all instructions.
Personally I would skip the etch primer, and go with eiother of the systems/ primers I have mentioned......Fred