@paddy - welcome to the forum. Where are you located?
I added a storage compartment many years ago. It's a wonderful upgrade and I highly recommend it.
There are several threads on this forum that detail this upgrade from multiple forumites. Search and you will find more details.
The deck extension is made up of three parts. See pic below for more detail. The base is a bracket bolted to the floor, two or four bolts, can't remember. The other two pieces are decking that can be removed individually. Only about 26 bolts, not that bad.
Lastly and most import, not sure where you are located but this deck extension configuration is only for US based sales. Our friends to the north in Canada have indicated that their vans have this extension welded in place. I'm assuming that holds true for all sales outside the US, included Europe. The reason is because Ford wanted to skirt the Chicken Tax on imports to the US and needed to quickly be able to convert a wagon config for 2nd row seating to a cargo model. It wouldn't make sense building the van in the factory this way otherwise.
Best of luck!