2014 f150 supercab sub box
 

Need plans or dimensions for a single (or double) sub box to fit on drivers side of a 2014 f150 supercab (extended cab) with 60/40 bench seat. Every box I've tried won't fit so going to build a box but don't know where to start with sizing.... Help? Pictures of anyone else's build would help also...thanks in advance

Do you have a sub picked out? do you know what volume you need to acheive?

Find the manufacturers suggested volume and take some rough measurements and see where it gets you.

Just Length x Width x Height (in decimals of a foot).
Example

15 x 18 x 12

(15/12"=1.25, 18/12"=1.5, 12/12"=1)

1.25x1.5x1= 1.875 cu ft