undercoating inside the doors and sound deadener

My 73 RR has intrusion beams and the factory undercoating in the doors. The undercoating doesn't extend to the bottom of the skin. A few of my own personal opinions: I hate that stick on sound deadener stuff. If you ever want to remove it, it's a royal pain in the azz. With the factory undercoating intact, I doubt there would be any audible resonance from the door skins unless you have a megawatt sound system. On the inside of my Duster quarters, I scraped off the old gooey factory undercoating and , after priming, applied a paintable aerosol chip guard . 3m Rocker Schutz works good but requires an applicator gun. For rustproofing in the door seams, I like 3m cavity wax. A lot of old undercoating will crack and separate from the body, allowing moisture underneath. It seems like the biggest noise issues with the old cars is wind noise. An otherwise super quiet car can make those little whistles even more annoying.