Gluing phase plug extension(now) while I can get clamps in, and reach it for sanding flush. Cutting damping material - seems like a lot! I'm assured that I need to cover all flat surfaces. My issue will be actually applying glue, then installing through the back. The fit is so tight, I may run it without glue on the inside panels (its not like they're going anywhere) and just glue the ones closer to the back. The "fingers" on the foam act to hold the adjacent piece in place, in two directions. They're also a tiny bit oversized so they'll get smashed into place. That's the plan anyway.