The design is a ported enclosure using an MTM configuration. The optimal
enclosure volume calculated for both sealed and ported alignments (using Unibox)
is well out of reach (684 litres and 618 litres respectively). The largest I am prepared to
live with is around 100 litres.
Bracing is not shown in the diagram.
I am a firm believer in slot ports. I prefer the look of them, but more importantly they
are much sturdier and actually add to the bracing of the enclosure.