I have a fairly large box tuned to about 29hz for my 2 JBL Gti's(12 inch). The port is in the middle, and it is double baffled. I noticed a couple weeks after i got my new amp my subs were sounding very "muddy" and didnt have near the intensity they did before.So i checked on the back of the box and noticed that 2 screw heads were out, i pulled them out by hand and they were broke in half! Keep in mind these are 1 3/4 coarse thread drywall screws that were pre-drilled with a counter sink bit as to make sure the mdf didnt split.Since then I just havent had the bass up at all, and i can not really afford to have someone build me a new box, and I dont really have the proper tools to do it myself at this point. So I grabbed some bondo from work and made a layer across the seem of the back of the box let it dry and tried it out again, about 3 seconds of awesome sounding bass then it went right back to sounding muddy, as it turns out the bondo popped off right at the seam across the back of the box.SO my question is, is there any relatively cheap way i can reinforce the back of my box so this does not keep happening?