Box specs for 4 15" BTL's?

[Basshead 3]

i am going to get 4 15" fully loaded BTL's and was wondering what the best box to put them in would be. 5 cubes by themselves with a port? i always heard it's best to put them in their own box or if it shares a box, to put a separater to separate the subs. but lots of vehicles i see on here lately have 2 to 4 subs in one BIG box. any differences in the two? i saw steve meade (i'm sure you've seen him) fit 4 18's without walling his suv, so i'm hoping it may save on space to fit the 15's. i have a lil more than 20 cubes of airspace available. nothing bigger than 42"W x 33"H x about 40" long.

if possible it'd be nice to fit 4 18's, but the chances of that happening with my space are most likely limited

can anyone help me with box/port dimensions? i just want the best build possible. if you can i'd love you forever

[Basshead 3]

oh, and it's going to be used as a daily driver, but i want to compete. maybe a removable port be necessary?

[Fi Car Audio 64]

This is going into an SUV? How tall is it to the back of the seats? Ill shoot for (4)18s as you are sitting at 28 cuft right now, but if you only have 20" to the seats youll be down to (4)15" territory.

Also is 33" high to the roof?