Just finished using POR-15 on my monster tank.... Very happy with the results!
My tank I got off eBay for a new project only to find it was very rusty inside to the point I was thinking of getting another, but figured why not give this stuff a try. I cleaned tank twice, first time it produced nasty black gunk, rust/scale. Second time was much cleaner and seamed to get rid of the rest of the rust/scale. My only issue was with my tank, which does not have the removable inner filler neck making it almost impossible to see the inside of the tank. So with this kit I tended to overdue each step to ensure I cleaned, prepped and coated the entire inside.
Do to the amount of rust I had and overdoing each step it took pretty much all day to finish but I'm please to say this worked perfect, very happy with the results! Thanks for posting this as I would have never even thought of coating the tank before this.