AeroGel

http://www.jetsongreen.com/2010/02/aerogel-ultra-thin-super-insulation.html

Sheets of Spaceloft are available is in sheets from .2 to .4" thick.  These are very expensive. I do think it might be useful to clad with cloth or leather to provide extra ceiling insulation.

Aerogel is the highest insulation value material available.  It provides R-10 per inch.  I plan to use it for a thermal break on the metal wall studs.  It cost $1.99 per inch for a thin piece of tape.  If I use closed cell foam to seal the walls and fill those cavities, it seems smart to attack the next culprit of heat loss, the thermal conductivity of the wall studs.  This material is called Thermalblock.

Each of these Aerogel products are mostly air and as a result are extremely lightweight products.  I find them interesting for automotive applications also.  A thin sheet of this material would do much to thermally insulate a car.

The insulation of my floors were simple fiberglass bats.  That seems to make sense for a floor to allow for moisture to escape out of the bottom of the camper.