FWIW: Just one opinion based on many past POR 15 experiences.
In support of reply no. 3 above, and definitely not to be critical of failures experienced with POR 15; but, absolutely without a doubt if one continues to ask experienced POR technicians and very experienced POR 15 salesmen, they will "all" tell you that most POR 15 failures occur when POR 15 is used by professional and experienced painters; and also non-professional and non-experienced painters, who fail to not only read, but understand the POR 15 directions ...... which I might add, as POR 15's fault, of not always printing and explaining in "detail" what "NOT" to do.
All highly technical industrial paint manufactures today never use the word "Paint'.
"Coatings is the word for these very "different"materials that one "cannot" find at Wal-Mart, where one usually finds cheap paint stuff like: "Buy one ... and get one free."
Good examples for POR 15 failure:
A. Apply POR 15 in high humidity.
B. Clean metal with acetone, lacquer thinner, paint thinner, gasoline, etc. which dissolves oil and grease and allow it to enter porous metal ....... also, using soaps leaves a film that POR 15 will not adhere to ..... hence, use POR recommended Marine Clean or nothing and treat and etch rust and SS with materials per POR directions.
C. Buying large cans, using little, and coming back later to find a rock hard mass inside the can. (Using six packs of small cans works far better for Model A hobbyists.)
Using POR 15 is absolutely 100% opposite and totally different from grandpa painting a toilet seat with tough enamel.
My Coupe chassis on my 1930 chassis is like new after 20 years with POR 15 and POR Chassis Black over sandblasted and properly prepared rusty and pitted steel.
I painted undercarriage, under side of fenders, brake rods, and everything under my 1930 Town Sedan and still looks great after 6 years ..... rocks hitting underside of fenders cause no harm to the parrot beak resistant POR 15 Chassis top coating.
I think it would be far more helpful for POR 15 to print: "What "NOT" to do rather than allow users to find out the hard way.
Like the so very few who use it successfully and claim to like it, I found out and learned the "hard" way by experimenting with POR failures.
I never blame users who condemn this material ...... it is "NOT" just paint .... appears it will outlast one's lifetime or more than one (1) lifetime, but it requires special precautions and knowing what "NOT" to do.
Some just do not have time to learn POR 15 through experimentation ..... very understandable ..... they should be respected for finding other solutions.