I'm not saying that there aren't plenty of good products out there but my experience has been with POR 15. I'm guessing that Ospho is very much like the POR metal ready which is a mild phosphoric acid solution as far as I can tell. I am building a 1940 Ford pickup and have been using the POR products on it. I have some panels that I painted with POR 11 or 12 years ago and have never has them rust again yet. You can literally paint over rust with most of these products. The surface prep required is often refered to as a PITA by everyone but hey, you're asking a lot of this stuff, the least you can do is prep and apply it the way the guys designed it to be used. The key property of most of these products is that they effectively seal the metal from any further exposure to oxygen, inhibiting corrosion. I know in the case of POR 15, if you aren't painting on sound, rusted surfaces or nicely sandblasted or properly etched by metal ready, the stuff will peel off in sheets, except in the case of your hands, where it will stay on good and strong long enough for you to be explaining it to your grandchildren. Also as was mentioned, the POR15 paint is a bear to seal and re-open. If you get any paint into the groove of the can, it will "weld" the cover in place. Use care in dispensing and take out a quantity to paint with, put plastic wrap between the can and lid. Use the paint that was dispensed from the can for your project and discard the rest. The product is a moisture cured urethane and it hardens by interaction with the moisture in the air, you want to minimize the amount of time the can is open. To help in this regard, POR sells the product in little 6 packs that are great to work from.