I am looking to install (2) JL 10W3v3 subs in my Dodge Ram with a custom enclosure. It has been 15 years removed from stereo equipment and my brain does not work like it used to. Would someone please tell me what is the total cubic volume needed for these subs. The JL audio web page says that the net volume is 0.625 cu. ft. / 17.7 liters. I am guessing this means the size of the sub. Does this mean I have to subtract this number from the total cubic volume of the enclosure being built? Also, what is the optimal cubic volume needed for these subs to be tight and crisp?