Given the NHT1259s requirement for 2.7 - 3.3 cubic feet of enclosure, I wanted to maximize it without going overboard in any one dimension. The minimum width was dictated by the driver, plus a little fudge factor for adding mounting hardware, etc.
So I settled on interior dimensions of 12.5" x 12.5" x 40.25", which gives 3.6 cubic feet. Factoring in the bracing and driver displacements results in 3.3 cu.ft.
Since 1" MDF was not easy to come by in this little berg I live in, and since I wanted a nice finish on the boxes, I used 3/4" MDF with 1/4" veneer ply composite. Edges and base are 3/4" solid hardwood pieces, edges have 3/4" radius.
Outer dimensions end up at 14.5" x 14.5" x 44", including the harwood pedestal, but excluding the stonework top piece (since it's not done yet).
The narrow width allows the side walls to act as front/back bracing for the driver frame. As added bracing, I used 1" sq. wood bracing in a box configuration all around the driver, and at all MDF joints. The top part of the box has 3 front-to-back and 3 side-to-side staggered cross braces.
Felt was also hard to come by, and the stuff labeled "speaker felt" is expensive, so I chose to use roofing felt (suggested by a BASS Lister). Three layers of 30# felt on each panel.
In the lower portion, immediately around the driver, I added some convoluted acoustic foam (left over from another project 10 years ago).
Final stuffing is with 2.5 lbs. of Holifil II (JCPenney King size pillows).
Drives are mounted with 1/4" allen head bolts to threaded inserts.
