So, I have the bulk of the gluing done. I have a bead around all the inside edges, and I've glued in all the primary braces. There are four front-to-back, two side-to-side, and two top-to-back. The top panel is going to be partially braced by the shelf port assembly.
Hopefully this amount of bracing will be sufficient to prevent resonating panels. We'll find out after the glue cures, and I wouldn't be surprised to find I need a couple more on the bottom, top, and shelf panels.
PL Premium is the go-to adhesive for speaker cabinets, as it expands while it cures to form air tight seals. It is fairly nasty stuff though; the tube says it's okay for indoor use, but the offgassing is fairly odorous so I can't imagine it being used in anything besides original construction. All the braces are screwed also, so as long add it does a reasonable job, this thing'll be rock solid.