May be you're right...kinda hard to tell where it's all going.
I'm still puzzled by the avatar change to that of a bullet...kinda unusual, especially for an audio forum, but maybe he's building an indoor shooting range, and that's what the soundproofing and 10 layers are for...?
Around here...we just go out into the woods for some target practice...though you guys in Texas probably are less concerned about where you shoot!
I have pondered that design approach...the use of a hard/plywood layer to create a resonant absorber. I know back in the day Ethan Winer, designer of the "Real Traps" products, use to have plans on his website for making large resonant absorbers out of plywood sheets of different thicknesses...with each thickness and overall size targeting a specific LF to treat....then he came up with the Real Traps, and kinda moved away from them.
The resonant absorbers were/are a very legit way to control LF...but you needed a lot of space, and you needed several of them at different dimensions in order to properly cover the whole LF range...or you could use just one LF target panel if you had a specific LF issue.
They make smaller traps these days that incorporate some sort of limp mass like with MLV, or a tuned resonant surface, both of which work well...but they are harder to build, since the layers have to be properly sealed to work right, and you have to get the absorption stuff right, since it's all one system.
Acoustic Geometry makes some cylindrical traps of that nature...that also provide diffusion due to their cylindrical surface. I've been considering a few of them.
I have a bunch of deep LF bass traps I made a couple of years ago...but I didn't include any hard/resonant layer, other than have one side of the trap with the foil-faced fiberglass board, and the other side with just the soft fiberglass...with a total of 6" fiberglass panels. I plan to stick two of them in each back corner, angled across the corner...and I was considering about adding some additional limp mass or resonant LF trap behind them...like a double trap approach...which I think should significantly absorb the LF buildup in the corners...but I have to do some more research...it might be a waste setting them up like that, though of course, I can try it a couple of ways if I get the cylindrical traps...and see what sounds best.