I just bought a single 10" box from Supercrewsound. I just did a test fit under my rear seat, and the seat would not fold all the way back down....it was a few inches high. I double checked that nothing was in the way and everything way in the right position, and it was. I called SuperCrewSound and the guy I spoke too said he has the same truck and had the same issue. He said to pull the box out an inch or two and then give the seat some time to settle, and then I should be able to get it folded back down.

Has anyone else had this issue or is it just me? Anything else I can do?

 

You could lift the seat up 3/4" to an inch. Check around in the forum, I'm sure that someone with an 04/05 F150 has lifted the rear seat.