If you want to be 100% sure that you have consistent adhesion and no rust creeping out later, I would recommend that you epoxy prime the parts right after they come from the paint stripper. Keep them in a dry place until you can work on them further.
No better advice has been given on this topic.
"etch" primer is a catch phrase for sticky primer... think about it... what good is a primer if it ISN'T sticky.
There is NO replacement for epoxy primer regardless of brand.
Bare metal needs epoxy primer to prevent rust creep. Rust Creep describes the ability for rust to creep under coatings once it starts with a scratch or chip. Just look at powder coating that's been chipped or scratched... that's "rust creep". Epoxy primer over bare steel is ONLY rust preventive coating.
