I'm using Nason products on my bird and their instructions say that you can use their epoxy primer either with or without etching primer, but advise not to use etching primer over anything but bare metal. I know that last fall, I got some etching prime on some paint in one door jamb and it lifted the paint. The areas that I used the epoxy primer without using etching primer first still look good - no lifting, etc. They also say that metal prep is not necessary if you primer right away.
Why do we never have enough time to do it right, but we always have enough time to do it over?