Now you can research and discuss insulation until the cows come home. I know, I did it. In our travels we ran into a gentleman that produces specialty vehicles (ambulances and such). He also has an extensive history in the RV industry. He recommended Radiant Technology. It’s radiant technology but doesn’t require the air space like some other radiant products. It comes with adhesive on one or both sides. I inquired about our project and discovered they have a pre-cut kits for several vehicles including the Ford Transit. I opted for the kit and very glad I did. It’s also known as the pink stuff. A great company to deal with.
http://www.radiant-technology.com
The Double Down
We were also looking for additional sound insulation. We opted for Thinsulate. A shout out to  Morey’s In Transit for their installation tips and tricks. http://moreysintransit.com/
The pics below show most of it installed.