I'm not to sure about the dynamat, that is mostly for deadning troublesome vibrating panels, you need something like fiberglass, I used some 1" thick "batting" I picked up at an upholstery shop, better than fiberglass and no itching.
Do you have a link or pic of what you would consider ideal/optimized window bracing? If I understand you correctly, I could draw up another model and compare the two. Either way, the large (and thin) port tube needs to be supported by the braces and that requires a significant amount of material.I'd have to believe window braces are the most efficient use of bracing if trying to minimize displaced volume. Braces with holes cut in them aren't efficient uses of space and add a lot of unnecessary work.
The outer edge of the port tune is 5 inches from the interior rear wall. It's about the same distance from the back of the driver. There is 11.5 inches of space from the end of the port tube to the side wall that it "points" at.Not having at least 8" of clearance from the port opening is definitely a problem you should concern yourself with, as it can result in early onset of compression. How much clearance will you have as it is designed now?
Be carefull if you're using less power than the drivers are rated to handle. Running a clipped signal into the drivers will burn them up very fast.My only concern with using more power would be cone excursion, possibly bottoming out the driver, especially with the 14.5 Hz tune. I'm going to start out with 500-600 watts mostly because that's what the amplifiers I already have sitting here will do.