water bubbles in paint

I have a 95 Windstar. It shows its first signs of rust, a few bubbles in the paint, filled with water. I have sanded the paint away to find shiny metal with tiny pinholes of rust, going through the metal. I have sealed
the inside of the wheel well with a tar-like paint substance used for corrosion protection in submerged surfaces in industry. I have kept the vehicle dry for many days prior to repainting. I give it a spray-can paint job (which is acceptable in color match). The water bubbles reappear within days. Each bubble has a good sized drop of water behind it. I have tried using primer, extend rust converter, body glaze. So far, the longest it goes is five days before the water bubbles reappear. I have done this 5 or 6 times now. What the heck am I missing here?
-- Denis Roy D. Roy Woodcraft www.ideasinwood.com
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Unless you sanded the inside of the wheel well down before applying the tar then thats where its coming from.

paint
within
or
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