I used a product made by the makers of Lizard Skin on the inside of both the roof and firewall, then put Lizard Skin over it in accordance with the manufacturers recommendations. I also put the Lizard Skin on the walls and inside the doors to further reduce noise. Can’t recall the name of the other product but it had ceramic particles suspended in it to reduce heat transfer. Worked great. The sound created by tapping on the roof went from a ringing to a thunk.
