SLOWING down the rust monster..........
When I first got my E-Body in 1978, I lifted the rear trunk mat and noticed it was wet underneath. I was the middle of summer and it hadn't rained in months. I pulled all the lower fender plugs and flushed them out good with lots of water. I had to use a coat hanger, sized wire to reach into the cavities and break up old leaves, twigs and other organic material.
Once I saw that the water was running out clear, I moved on to the next panel. The trunk floor had just started to get rust on it and my cousin had put the battery in the trunk. The acid from that battery had gotten down into the rear quarters. I flushed some baking soda through the area and rinsed well.
A few days later after the car had sat in the hot sun, I treated everything with Ospho from a marine supply store. Then primed and top coated the areas I could reach. The car remained virtually rust free after that.
I also removed the factory sealant along the firewall to inner fender well. I found rust had formed behind the foam-like sealant the used along the pinch weld. I treated and resealed that too. I never put that vinyl trunk mat back in. It seemed to always have moisture under it.
Cleaning and treating the cavities in the lower quarters, trunk and front cowl turned out to be a much wiser thing than throwing away that ratty, old slip of paper with jibberish on it that I found under the front passenger seat.