@gladmo: NoRez is a great product. Since I built sealed enclosures for the Rythmik 15" kit, I braced the Hell out of them: 1.5" x 1.5" Baltic Birch ply braces (doubled pieces of 0.75" x 1.5") every 6" inches, in all three planes: front-to-back, left-to-right, top-to-bottom. The braces take up a lot of internal volume, so the boxes ended up being rather large (for 15" subs): 24" tall and deep, 18" wide. When you do that NoRez is not necessary.
Danny Richie recommends NoRez for even his GR Research open baffle subs and loudspeakers, on the large unsupported (structurally) panels.