I've been using Zero-rust, and I like the results so far. The only thing that I have any concern for is the fact that it takes a few weeks to really harden. Some of this could me my fault for spraying it too thinck, but the manufacturer says that it seals so well that it seals itself from drying quickly. It's dries to the touch really fast, but you can still scratch it for a few days. After that, though, I have a lot of confidence in the durability. It's not as harmful to spray as Por-15 either.

http://www.mfgsealants.com/zerorust.htm



I have also used Picklex 20 which is a true rust "converter". It's about $70 a gallon, but it goes a really long way. It's a pretty safe product to use as well.