One advantage of epoxy primer over bare steel is the excellent adhesion factor that epoxy offers compared to lacquer primers as well as epoxy's sealing ability that blocks moisture.
There are 3 major advantages of epoxy compared to lacquer; it seals the backside from moisture which will extend the top coat life, you can apply filler directly to epoxy which eliminates the possibility of moisture absorbing into the filler from behind and epoxy is tough and sticks like glue.
