The only thing is that the wood is slick and probably move around on corners. You might want to take the hook part of velcro and staple it to the bottom. Just remember that the hooks will be tearing the rug up. You might even be able to use the green scrubby pads instead of velcro. Oh yeah dont forgete the pics hahaha

 

1/2" will be pleanty for those "subs" use wood glue and wood screws for the box (pre drill the holes for the screws so you don't split the MDF)... don't waist your time with carpet, go to wallmart and buy spray-on bedliner and coat your whole box (it will help seal it if you do it right)... once you are dissatisfied with the loudness of the speaker send me a pm and I will tell you where to get some subs that will destroy those kappa's for CHEAP...