Your dealer is wrong, it isn't going to "convert" dittily. It will "seal" out moisture from feeding the rust though. Epoxy is very sticky, that is it's ONLY quality. Because it sticks so well it protects the metal even when chipped. But etch primer will protect even more, IT does a conversion "sort of". It's acid bites the metal and is similar to a conversion coating that leaves a phosphoric acid coating. So etch then epoxy is the ultimate for corrosion protection. But again, epoxy is horrible to work with as far as sanding. It doesn't replace the use of urethane for surfacing.
