I ordered the third row seat for the FJ (
Little Passenger Seats - your source for custom SUV third row seating) and made a custom base for it so that I would have some lockable storage...plus I needed an excuse to get a welder
The box is all steel with 1"x2" rectangular tube for the walls and c-channel for the lid frame. I recessed the mounting hardware as much as possible in order not to lose any internal storage area. The front slide lock allows a pretty big padlock to be used to secure everything.
This frame also allows me to mount the seat rear facing for trail runs or forward facing for longer trips and daily driving.
Here's the box and lid after a second coat from a rattle can (after a base coat of primer):
With the lid on you can see the brackets that can hold the seat in place while the lid is open in order to reverse it and re-bolt it to the lid:
The base is bolted through the cargo area floor to the brackets that come with the seat. I left the top of the lid frame open in order to utilize the void that exists under the seat to fit my air compressor:
I ordered the storage rack and bags from
http://www.springtailsolutions.com and instead of mounting it on the rear door I was able to mount it directly to the steel frame in the seat, so it'll hold pretty much any amount of weight I might hang on it:
When I flip the seat around, the void between the back of the rear facing third row and the back of the second row seats accommodates the rack and bags:
There's plenty of room for all 3 of our kids (ages 8, 6, and 4) back there and I still have full access to the jack storage area:
