I don't know why the put the box on the truck.  Never did get a good reason from any of them why they use that configuation.  I have loaded a few of the trucks out of Joplin.  My last 3 years I worked with training the reserves.  We normally used about 75 trucks each way with their summer training.

 Never really been around an FMTV except to see them driving around when I was on Fort Knox.  Marine Corps bought the MTVR and the Army uses the FMTV.  The MTVR is heavier with a 7 ton cross country compared to 5 ton on FMTV according to Oshkosh website.  As far as a truck I like the MTVR.  It has a great suspension, the C12 and auto transmission work great together with a jake that really works and it has a good payload.  We had very few problems out of the ones we had. 

The one I would have like to saw fielded before I retired was the LVSR.  http://www.oshkoshdefense.com/defense/products~lvsr~home.cfm  I have watched the prototype in testing and think it will be a good piece of gear.  I got an email from a friend that said the new M ATV is a good vehicle also.  http://www.oshkoshdefense.com/defense/products~matv~home.cfm  He has 10 days left in country and said he got to go for a ride last week in one.