First off do not Build a 60hz "spl " box ... it wont necessarily be louder ... Tune to where your box peaks at the Fs of the Focus . Your going to want to run Aeroports not a slot due to better efficiency ... Look at Terry Brocks build . A bonus with Aeros is that you can make them interchangeable . ...
BOX TIPS :
1 round all corners on the outside of the enclosure
2 Resin the inside of the enclosure and outside
3 do double layer 3/4" birch or mdf
4 front baffle 3 layers
5 use 1/2" all thread as your bracing .
Current : 2 15s 149.5@56hz 2k rms Previous Trunk box 1 18 ,146.4@43hz 3500rms,Sony 12s 145.6@63hz