Rear Wheel well lip rust, need suggestions

Painted my car and some bubbles developed on the rear wheel well lips. I sanded this area to the factory primer and went from there.well a year later and I have rust bubbles. A few spots have rusted through( about the size of of two pencil leads side by side is the biggest). How should I go about this? Not big or bad enough to cut out and I can't get to the back side from inside the car. Thought about taking a syringe and squirting phosphos into the pin holes and the back side of the panels the best I can and then the same with Por-15. Any suggestions?