Nearly every time another sound deadening posts crops up I tout my own best solution which combines cost effective and permanent application that solves more than a few problems associated with bare uninsulated vans. To wit: http://www.radiantbarrier.com/double...insulation.htm
I've used this material on four different E-Series vans and its been outstanding each time. It provides insulation of course (albeit a bit minimal comparatively) but sound deadening and almost total elimination of bare metal condensation is a huge benefit.
Using a 3M-type spray adhesive there is no residual smell and for the most part this stuff is quite inexpensive. Because its a stable non-asphalt material it has absolutely none of those qualities, perceived or actual. Since its insulation it can and does easily withstand temperature swings because its designed to do so.
With a single roll I can double-layer cover and entire E250 EB and still have some left over---all for $150 or so, less adhesive of course. Its easily cut and shaped to fit to most any flat or curved body panel including inside door shells, even the front doors with movable glass. After installation it requires nothing as far as upkeep etc.
Perhaps a bit smugly I chuckle when this topic is raised anew----I'm trying to spread the word on a great alternative to FatMat etc etc et al. And NO I'm NOT associated with ANY radiant barrier insulation manufacturer or seller!