Will be using 4 Skar MA8 D2's in my new setup. Having difficulties with the enclosure. Currently I am looking at 48.25" w x 20" h x 13" d (external measurements), with a 3" w x 18.5" x 30" l port. Calculators (Torres and Xplicit) show it to be 5.76cuft gross, 3.84 net (.4cuft displaced by subs) with tuning around 32-33hz. Does this sound acceptable?