This is a mod to allow your double cab rear seat back to fold. "Nisbo" a member over at TS did this mod. I decided to try it.
The tools required are a 14mm socket (a couple of various size extensions help). A T30 Tork bit (6 point star) and your choice of a hack saw, jig saw, grinder or cutting wheel.
I have the under seat storage tray so remove that if you have it. It is held on with four fasteners that you can turn with your hand.
Fold up the seat bottoms.
Now remove the six 14mm bolts that hold the seat in place. There are two bolts per seat support leg. Each leg has one bolt that holds it to the floor and one to the rear wall of the cab. (*You might be able to get away with removing the bolts that hold it to the rear wall of the cab and just loosening the ones that bolt it to the floor. I removed them all).
Once the bolts are removed, lift up on the seat assembly with the seat bottom in the up position. I did the small single seat section first to try it. What you are trying to do is lift the seat back enough that braket that hold the seat back in place clears the metal loop in the wall of the rear cab. You can see these loops in the below picture. They are body colored. In this picture the seat back has been lifted and unhooked.
At this point I reinstalled the six 14mm bolts in the three support legs. Do this, but leave the seat back folded forward.
Then I removed the four brackets that hold the seat into the loops. The Tork (star) bit is needed. I have heard that some folks have cut the bracket in place, but I did not want to do it that way.
In the below picture the loops on the cab wall are highlighted in red and the brackets are highlighted in yellow.
These are the bracket once they are removed.
I cut about 2.5 cm or 7/8 inch following the contour of the original bracket.
This is a before and after comparison picture.
Here is a size of the cut comparison.
Once the brackets were cut (I used a hand held grinder and a vice) I used a file to remove the rough edges and used back spray paint for a finished look.
Now you reinstall the brackets. I suggest hand tightening the brackets to do a test fit. The way you operate the seat back is that you fold up the seat bottom because this raise the seat back as well. It should raise the seat back enough to clear that loop highlighted in red above. Then when you lower the seat bottom, in lowers the modified bracket into the metal loop to lock the seat back in place. You can also still lock the seat bottom in the up position as well; just raise the seat bottom as normal to until it locks in the up position.
Go fold up the bottom of your seat to see the motion I am trying to describe.
Here it is folded down.
The seat backs still lock in place for normal use and there is no worry about the seat coming forward un-intentionally (I guess that is possible if you cut a lot more off the bracket that I did.)
The finished product. Don't forget to tighten the Tork bolts after your test fitting.
I might add some plywood or some solid surface to the back of the seat to cover the foam.
I wish I had done this mod before installing my seat covers...it would have made life easier.
All in all it took me about 1 1/2 hours because it was about 95 degrees today and I took cool off breaks.