need some ideas

[PMAC]

i agree with the 1/4 mdf i am a former cabinet designer and builder and figured the mdf might not hold up for long it was basically just a temporary solution to get me a average system until i could afford to go all out. the airspace is a very large factor due to how the back of the cab is designed. The 2 rear speakers are incased in the interior molding but they stick out about 3 to 4 inches from the back thats why i couldnt extend the box to be the full length of the cab, plus the sub isnt really "top of the line" i really wanna go to a solo baric kicker or sumthin that airspace wouldnt have such a large factor on.