Alright, I looked up that sub and I think I know what you need. First and most importantly every sub woofer enclosure is different-made for the sub woofer you will be using. Unless you have the same exact model DYNACORD is using, your box will be slightly different. In fact depending on the sub, your box may be dramatically different. There are some people, like myself, that could help design an enclosure for you but they will probably charge for their services. Either way you can go on the internet and look at some designs to give you an idea of what you need to build. The particular design DYNACORD chose to use is called a "Vented direct radiating cabinet" (it also uses a couple other electronic goodies) a little complex to understand and build. Sure you could try to copy it but it won't work right unless you have the same sub. In fact I use a computer program to assist me in this regard, so don't feel bad if you don't get it right the first time. Good luck and I'll leave you with something from Dynacord.
-Dynami

DYNACORD´s COBRA-SUB is a vented direct radiating
cabinet, equipped with the high-power Electro-Voice EVX
180B 18" transducer.
Frequency response is 38Hz - 170Hz (-10dB), so the crossover
frequency to Mid-Hi cabinets, e.g. DYNACORD´s
COBRA-TOP can be chosen strictly application-oriented
between 80Hz and 160Hz.
The cabinet is equipped with an electronic circuit called
VOICE COIL TRACKING PROTECTION. This circuit senses
the terminal voltage of the transducer and simulates the
thermal behaviour of the woofer´s voice coil. In case of
potential thermal overload the power applied to the speaker
is reduced to a safe level.
Power amps up to 1200W/8Ohms can be used in order to
have maximum dynamic range without the danger of thermal
overload in non-controlled situations. The VOICE COIL
TRACKING PROTECTION exhibits “soft” switching characteristics,
so no annoying clicks or pops are audible. The
circuitry automatically resets after the voice coil temperature
has reached a safe value.
The COBRA-SUB cabinet is made of 18mm birch plywood.
All corner joints and braces are grooved and glued. The
cabinet´s surface is coated with an extremely durable Polyurethane
which exceeds the quality of a standard lacquer
finish by an order of magnitude. A powder coated steel grille
and a lockable cover protects the COBRA-SUB against
damage during transport and bad environmental conditions.
The connector panel uses two 4-pole Speakon connectors
(IN/OUT) for a safe connection and easy daisy-chaining to
other cabinets. The pin assignment is 1+/1-. Pins 2+ and 2-
are also connected between the two Speakon connectors.
When using DYNACORD power amp racks, the whole system
can be wired with 4-pole Speakon cables without any
danger of accidental wiring mistakes. Four recessed rigging
tracks and two webbing-strap points can be used for easy
“flying” of the COBRA-SUBs. The cabinet is equipped with
four large ABS feet that allow easy stacking and a “snap-on
flying” even in angled positions.
Two handles and four heavy-duty castors on the rear side
guarantee easy and safe transport.