Certificated a/c, inexpensive epoxy primer, autobody?

I have a certificated a/c (rag and steel Tcraft). I'm considering the
Superflite I covering system.

Since the Superflite system apparently doesn't begin until the 'apply
the cloth' stage, I'm free to use any primer. I'd like to use an epoxy
primer since I've seen what condensation did to my steel tubes.

So I'm looking for an inexpensive epoxy primer. Am I restriced in what
I use since it's a certified a/c ? Must I stay away from the auto body
shop/store? Suggestions?

- Mike