I think a better test would be to use a small ball peen hammer. You should be able to tap the the metal and not put a dent in it. Tap where you have good metal then compare on a small hole. You will see and feel the difference. ? Did you drop the gas tank and look at the bottom on the trunk? If you want the repair to hold this is necessary. To do it right is a lot of work but not requir the technical expertise of a floor replacement. When I did mine I cleaned both sides of the floor, ground back to good metal at all of the week spots and holes. Then did the metal prep according to the directions. Make sure to let the trunk is really dry. Then I did a POR fiberglass layer on all the holes from the bottom side and let that dry. Did the top side glass next, if you need more strength add more layers of glass. Then finish coat both sides. This will not give you a show finish but should be a good stong dependable floor. Hope the project goes well.
POR 15 trunk kit I used it on the 70 lesabre. Unfortunately I also blasted around before I took the picture but minus the sand it looked good. http://www.camaroandmustang.com/trunkrepair1.jpg
