Nothing wrong with reviving old threads, they often contain gems of wisdom that might otherwise be overlooked by members later to the forum.
I use a product called Trailercoat, discovered it back in the late '80's searching for something to use on a boat trailer regularly dunked in saltwater. The axle had gotten very rusty. I used a combination scraper/wirebrush to knock the loose stuff off and gave it two coats. After eight years of saltwater and salt sea air exposure it finally started to discolor a little here and there. Dries tough and hard. A bit expensive (last one I bought was about $35 /quart) but it has proven itself to me (and a number of others I've recommended it to). The only "drawback" I can see is that it is silver colored, but it does lend itself to topcoating.
http://www.pettitpaint.com/product.asp?id=96
I tried POR 15 once and was ultimately disappointed. Probably didn't jump though all the hoops it requires, but did use it on a very clean, well prepped surface-----most rattle can paint would have lasted longer, in my judgement. Very little exposure to the elements, always garaged, and it eventually cracked and peeled. I did not use any primer under it.
