Say My box is 16 x 16 x 13 On the outside using 3/4" board Its bigger then 1 foot volume right, So what if I drill some wood inside the box down securly and out of the way of the sub to displace the air in there. Is that a problem? Would be easier then spending money on a new sub box.
You shouldn't have to worry about bracing a little 1 cf sealed box, as long as it's 3/4" MDF.
You see bracing more when your dealing with a really large box and a heavy sub with lots of output. Something like a 40 lb sub in a 5 cf ported box. Then you'd definitely want to consider bracing.