Just used POR-15 for the first time and was very happy with the results. Used a piece of exterior exposed galvanized sheet metal as a test case (a/c duct transition box). I was absolutely impressed and plan to use it on my kit as well. There have been several posts on it's use and misuse. Please heed this advice:
Do not attempt to circumvent their instructions. To do so will invite failure (gee what a mess) of their coating to properly bond. You must use their pre treat materials. Also, if any parts are exposed to UV, you must use their paint (they do say others will work, but the additional post prep isn't worth it). Failure to paint exposed pieces results in a powdery finish you won't like. Also, exposure of the can to air will ruin whatever is left over in the can. Buy the 6-paks so you can use alittle at a time.
Good luck it is a great product when follow their instructions.