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Looking for something that will work with standard primer/paint coating



Personally I would use the factory method and call it a day. If you do proper rust removal, metal prep, and apply the primer, sealer (zinc chromate, etc.) and paint it like the factory and did you should have no further worries. Nothing on the market will fix short cutting rust removal, cover it all you like, it will come back eventually.

On a side note; I wouldn't use POR15 on my lawnmower.