Well looks like steel wool was the secret weapon in this rust removal process. It worked very well to agitate the rust and allow the acid to eat it up. Also paper towels worked great around the edges to keep the acid in place and maintain wettness. One gallon of phosphoric acid is enough to do an entire roof.
I still need to remove the trim between the roof and the quarter panels and remove the windshield to clean out those edges and the ones around the rear window with a wire wheel. Then do a final once over of the whole thing and prep and clean it for primer.
