I climbed under the car to grind away the surface scale from the bottom of the trunk area where the gas tank covers. That old original metal is pitted an had some small holes here and there so no sense it trying to remove all the rust down to shiny metal as it doesn't exist.
So once all the surface rust was removed, it was wiped down with some thinner to remove any grease and oil, and then I applied some rust converter.
Also since it has been a few days now, I could paint the inside of the trunk where I had put down the rust converter previously. Eventually, the trunk floor will need to get replaced, but that going to be way down the road.
I also have the gas tank a new coat of paint and painted the filler tube.