well if I was in your shoes, I would purchase Eastwoods 2 part rust killer and follow up with either there rust encapsulator or the por 15.
both after the rust converter will work.
But I would first hit it with the rust convertor before I coated with anything.
Just my 2 cents.
Tim


1952 Chevy Shortbed

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If It Aint Broke Fix It Till It Is!