So I just now came across this old post. Last weekend, I pulled out the entire rear interior (everything behind the seats) from my 2015 TC LWB van (no windows at all, for reference) - and I took a ton of pics along the way. Hopefully this link works right, I created an album in the gallery with all the pics. http://fordtransitconnectforum.com/gallery/album/168-custom-build-out/
Hopefully this will help you or anybody else that's considering building storage into that wasted space. The bolts on the floor are all T40 aside from the cargo tie-down T50 bolts. My build will be slow going due to lack of money, lol.