I just jumped in here a little late on the question at hand, but me and my cousin were layin some paint on a 57 wagon that the fella just couldn't get straight. On the roof (and there was alot of roof!), the existing rust pits kept showing back up in his paint about every 2 yrs. after he got it painted (this was his 3rd shot.) We actually worked the roof a tad more and coated it in POR 15, then a thin layer of Rage Gold, and finished. 6 yrs. later and multiple car show trophies later, he couldn't be happier. Not one sign of the pits or shrinking in the whole roof line.