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Expedition Leader
How about a command box AKA Expando Van:
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Ward's (HealeyJet) http://forum.expeditionportal.com/threads/143852-Dodge-Ram-5500-motorhome truck box was built by Intercontinental Truck Body in Canada
http://www.itb.ca/about.aspx
Sister company in Washington TriVan http://www.trivan.com/truck-bodies-trailers/
A few more ideas (more DIY than prefab though):
This RV uses some really slick interlocking aluminum panels http://www.expeditionportal.com/forum/threads/125714-Ford-E450-4x4-build-revival?highlight=panel
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That last one is an ITB/TriVan as well. My truck is one of their bodies too. They are willing to build whatever you can think of if you want an aluminum skin.