Cotton VS Wool VS Synthetic (Polyester, Fleece and so on)

Now when its getting colder, avoid using cotton clothes when sleeping
Cotton sucks moisture from your breath and body and will get damped with moisture when humidity gets in your van. Low temperature also increases the relative humidity
Cold weather underwear (I think you call them that, in Sweden we call it “underställ”) often have a base of polyester or polypropylene. These materials absorb very little moisture and thus keeps the body dry and warm. A basematerial of wool has in recent years been increasing its market share. The wool absorb although moisture, but it heats (unlike for example cotton) even when damp. Furthermore wool underwear almost never smell bad and feels comfortable to wear even for extended periods of time without washing. A polyester underwear will pick up smell more than wool.
Keeping warm when sleeping:
Fleece Sleeping Bag Liners

Wool Blankets (ullfilt) (the inner core of wool fibers absorbs moisture (as much as 36% of its weight))
, long johns (underställ) and wool socks.


Other alternative:
Build a isolated triangle to lay in, use some cardboard for the “small triangle house” and dress it with insulation boards on the inside.

Here is an example with some pictures:
http://www.practicalsurvivor.com/urbansheltercoldweather