I used POR-15 to
paint my frame about 4 years ago and it is holding up well. But I have to say it wasn't a very pleasant experience. If you get it on you (and you will), plan on wearing it around for a few weeks. I couldn't find anything short of a wire brush that would get it of your skin.
I've since started using a product called
ZeroRust . So far, it appears to hold just as well as POR-15. It doesn't have the dangerous chemicals and it COMES OFF YOUR SKIN.