I decided to put some 1/2" thick neoprene on the inside of the firewall as a noise / heat barrier. The first step is to cut out some posterboard templates of the different firewall areas. This would have been a lot easier if I had cut these templates out before mounting the firewall into the fuselage.

Another thing that would have made this a lot easier would have been marking the firewall penetrations each time I drilled one (before putting anything through them). Then once it came time to install the neoprene it would have been a simple matter of just cutting it out and sticking it on.