and may not permit you to place sufficient damping material inside. Sound energy from the rear of the cone will be more able to bounce right back thru the cone instead of being absorbed, often complained of as "too forward a midrange" and/or peakiness. Instead of the dimensional ratio's used by Wayne, you could try Weem's suggestion (0.67/1.0/1.8) for a tall, narrow box. How many cu.ft. do you want/need? Samput a layer of R13 'glass at each end (top/bottom) of the long enclosure to help reduce/suppress standing wave generation...
orient the driver to insure that the solid portions of the basket are towards the walls if possible...