When I applied Dynamat in 2511, I got down to the metal floor, removed any loose paint and then covered with a high solids paint similar to POR 15.
I then applied a coat of thermal insulating paint similar to “lizard skin”
I applied a single layer of Dynamat to the floor area, and double layers of Dynamat on the center tunnel and engine firewall, as both of these are a large heat source.
I also added one 12 x 24 piece of Dynamat to the inside of each door, which made a very noticeable difference to the sound made while closing the door. Much more of a solid closing sound.
Larry