Just some suggestions, recess the side panels so you can "tuck" the carpet around, so the uneven carpet cut will not be prevalent. Cut the hole a bit larger, so you can wrap the carpet from the cutout underneath, so when the subwoofer sits in, it would create a better seal. I'm not sure what type of sealant you're using, but make sure use enough of the good ones. Use a good amount of wood glue, as that's what holds the box together, not the nails or screws.
Not all boxes need to be a wedge type. Sure, it may help with the phase cancellation of the waveform, but these are low frequency waveforms, with very large distance between nodes, so the likelihood of cancellation is very minimal and unlikely.