this is what the manufacturer recommends:
BL 18 – Ported box we recommend using 5-10 cubic feet @ 30-37Hz tuning, you can tune a little higher if you wish but we recommend keeping it close to 32hz for a daily driver. Again the same 12-16 square inches of volume applies per cubic foot of volume.
and its going in a tahoe. i wanted the box to be almost as wide as my "trunk" area, which is 47". so to have the box be 47", i chose 22" as height and depth to maintain some of those recommendations.
edit: i guess i could have also took the mounting depth of the woofer into more consideration when i built the box lol.... mounting depth of the woofer is 9.750”. omg and i used 22" lol... well i wanted to be able to have the box face forward against the cargo hatch or fire upward without having the box demensions be awkward if i turned one way or the other. so 22" either way seemed alright at the time. i hope it sounds good and slams, thats all im really concerned with. but this box has me nervous a little. i used re box calculator and have never built a slot port before.