That's a good article! ^ I've read through it a couple times now. Lots of good info!
Here's where we sit after this weekend. The HVAC box is out and i'm waiting on the replacement parts to arrive. Warrantying the heater core that started leaking after less than a year, also the Evaporator core while I'm in there. The A/C compressor is also getting replaced because the Clutch bearing has started making noise. Going to replace all the seals while it's apart. On top of that, I'll be wire-wheeling the firewall where the box mounts and completely refinishing that surface and resealing to avoid rain leaks that I was getting before.
What is the best sealant/adhesive/whatever to use between the HVAC box and the firewall to prevent rain leaks?
After getting the HVAC out, I started working on the sound deadening. Using Noico Deadener from Amazon. It's pretty good stuff for a fraction of the cost of Dynamat. I have friends that have been using it with good results. Anyways, I got the left wall and right wall behind the barn doors done so far. Going to be doing the roof skin tonight. I am pretty impressed with the results so far. Before when you would knock on the sheet metal walls, it would resonate and echo badly, but after putting this stuff on, that effect is greatly reduced.