Isolating the mechanical resonances is "technically" ideal, but NOT AT ALL practical; and it is really only needed for frequencies above 120hz. Midranges and mid-woofer type stuff; in particular where the basket or box is very thin and thus prone to resonance.
(B&W uses this mounting method on all of their 800 series mids for example, although done much more professionally.)
For such a tiny/weak subwoofer that much bracing is a bit overkill (but it doesn't harm anything), and he was being way too generous with the anti-leak sealant... a properly glued joint will not leak air!!!
That type of support is not even needed for a heavy XXX-18 or LMS-18 magnet, the screws will hold it.
For subwoofers with high excursion that dig deep, the moving-mass begins to increase to a point where the enclosure may begin to shake and walk about. This can be solved by making it dual-opposed or mounting it perpendicular with respect to the floor or adding more box mass or by adding feet that counter it with increased surface "sticktion" (or spikes that dig in).