RE: Winter Camping and Heat
The previous posts have covered all I can say (top down, down comforter) but
I can attest to the effectiveness of the Propex.  Mine was purchased from
and installed by Karl Mulendore and available here:
http://westyventures.com/propex.html
Mine is about four years old now and does not produce as much heat as the
current models but is more than sufficient.  I've used it down into the mid
twenties (Farenheit for my friends in the GWN) and leave it turned down at
night.  I turn it on and let it run till the internal temp gets to the mid
to high 50's, then turn the thermostat down till the Propex shuts off.  It
will then hold that temperature all night.
The only other tip I'd add is even if you don't have the special insulated
curtains some have made, close the curtains, all of them, at night.  Just
that small amount of trapped air between the glass and the curtains makes a
very noticeable difference in the drat of cold air inside the van.  Oh yeah,
one more thing.  That nice warm down or Thinsulate lined jacket you put on
in the evening?  Throw it over your feet at night, trap some heat down
there.