Yes, there is not very much heat, this is true.
But, here is what I have found:
If you put a sleeping bag over the entrance and sleep in sleeping bags, etc.,
there is a bit of heat that does come in. 
Behind the fridge, there is an insulated stove pipe.  In the winter, you
don't need the fridge to cool so much so I am considering removing this
pipe to allow most of the heat from the flame to be transfered into the
camper.  In the summer, stuff the insulation back in to let the fridge
work again.
Never-the-less, the heat from the exhaust pipe which goes into the sleeping
area is noticable just as it stands.  I have a hard time convincing my
wife also, so I sleep closer to the heat :)
We aren't really looking for much comfort, just a little bit.  It really
does seem crazy to have such a nice source of heat available and to not
use it.  
Oh, I have found that the fan will run slow enough with about a 300 ohm
resistor over the power input circuit.  The pipe will stay warm and the
heat will also come out constantly.  However, the pot which I now use is
a 400 ohm pot so that I can vary the speed from nothing to it's full speed.
The pot needs to withstand a bit of heating, but not much.  In addition,
the power consumption is reduced by a factor of about 1/3.
Stuart