There are many brands with many types of coating for you to choose from. Here are some of them:

Eco Tuff is a bit expensive, but it is recommended a lot. You may want to check it out.
http://www.dwellsmart.com/Products/Lumber-and-Wood-Products/Eco-Tuff-Clear-Coat

With this brand, it gives the colored coating from rusty to clear.
http://www.steelf-x.com/supplies.html?gclid=CJDF4LPKja4CFSYaQgod_GR-eA

This one is ok. However, since it is a spray can, it will be hard to do the detail work.
http://www.hydrogenappliances.com/marine.html

For people who work with automobile or machanic stuf.
http://www.cyclemaintenance.com/mechicscorner/cb750_finishing.htm

The last one is Epoxy. Some have been talking about this, too.
http://www.epoxyproducts.com/voc.html
http://www.epoxysystems.com/coatings.aspx

If you have any question, the link below will be helpful:
http://forum.woodenboat.com/showthread.php?65358-Waterproof-clear-top-coat-any-such-thing

By the way, Nyalic is mentioned in the above site. Look it up! It might be good stuff.