Epoxy Primer is great for preventing new rust on freshly blasted panels, but offers little to nothing over existing rust. You need to get rid of rust before priming and painting or you will be sure to see it again in the future. If you are dealing with a flash rust from the panels sitting after blasting then a metal prep wash will work. If it is anything more than that, I would either spot blast,or take a scotchbrite wheel to it or use a rust converter. But check the lables some liquid rust converters say not to use on blasted metal. Bottom line is you need to get it out of there, especially after all the work you have in the project to this point, you want it done right. You will be glad you did. Good luck.