There are of course chromate and zinc based primers for steel with rust inhibiting qualities that I have never been too impressed with. These are nowhere near as good as having the item zinc plated and putting a proper baked coat of paint or a powder coating over that.
Have a look at the transformer covers and black painted rear brackets and EHT cage on this TV chassis:
http://worldphaco.com/uploads/621TSARTICLE.pdf
Also, one advantage of power coating is that it can be made of a custom mix, if you look at the EHT cage on the TV chassis, it is a subtle dark metallic brown. This was done to replicate the original finish of the cage which had rusted. Powder coating is extremely scratch resistant and very long lasting, provided not exposed to direct sunlight. It needs to be applied by an experienced operator so that the applied coat is not too thick.