oops messed up on heading, it should say 2 12JLW3's

Alright i have a 2000 f150 and i have the 60/40 seat set up in my truck and i want to make a box that will fit behind the drivers seat in the "40" spot. I dont want to have to take the seat out, i want to be able to just fold the seat up and make it fit in there. has anyone ever done this? if so can i see some pictures?

If you would like me to post pictures of the spot to give you a better idea of my plans, i can do that. Also i need to know what types of materials i will need to make the box.