Seems to me your doing 3/4 of the major work and then using minor supplies...
You were on the right track getting stripped naked and putting some epoxy on.
Stopping at the old paint and primer is worthy of a 'Rustoleum' job but if that's what your after why even strip it that far? Just scuff and paint.

Get yourself to a few painters forums and search around and you'll find the difference in products is mentioned as well...


Give me ambiguity
or give me something else