UndercoverPunk
5,000+ posts
DOT
A well constructed box will not flex, and a decently constructed enclosure will not move beyond a slight "vibration" if you will.
If your box noticeably flexes, guess what, there's something wrong - plain and simple. Would you like to come see my box, you're more than welcome to see it NOT flexing...with a 15" avalanche and viper 1200.1
The the question at hand though, I would add a ring because as undercover stated you may end up with some noise that's not optimal. It was suggested earlier to add a complete face (ie double baffle), which isn't a bad idea for the cosmetics if you can take the extra weight. It will also help with flexing, but from the looks of it you're not dealing with long enough stretches to have too much trouble in that area.
B&W wasn't saying that it would flex ALOT, but simply that it will flex, which is what will cause that noise I was referring to.
