18" Evil is the thought at the moment, again open to any ideas
 
	Available room in the back for the sub box 42" wide x 28" deep x 18.5" tall = 13.61 feet of air 
 
	Now taking into account for the wood .75 thickness  40.5 x 26.5 x 18.5 = 11.49 feet of air. 
 
	Am I correct on this ? 
 
	Also what should the design of the box/port be ( sub firing back, port up... sub up/ port back ect...)