Dear Paragon,
I have looked at a lot of these. Many are made by companies equipping police vehicles. Te material I am looking at most closely is aluminum. I choose it because it has the thinnest walls and, therefore, yields the greatest capacity. Between the 2 drawer sides and the 2 cabinet sides, you can lose 4 or more inches of width. The one I’m looking at most closely is made by Huskyliners
http://www.huskyliners.com/storageboxphotos.html
and sold here
http://www.premierhummer.com/h2_custom_storage_box.html.
The one for the H2 should just be coming into production.