Noob needs help.....

Hello newbie here was wondering if you could help me...i have a 98 expedition and 2 l715's i wanna build a ported box for them with the speakers facing up and the ports facing up....i dont want stuff getting sucked into the port....is it better 2 build 2 boxes or just 1 because i do not want them to share the same air space as far as dimensions...24-26 inches deep 40-48 in wide and 18 to 23 inches high. i would like to have the maximum airspce closest to 12 cu ft if possible. i would like to tune it to 35hz and will brace it with 2x4's unless you reccomend wooden dowels or the corner braces.if there is anything eles you need pleas let me know. any help is greatly appreciated as i am trying to avoid buyin the commercial box of of ebay