For the incurable cheapskate tinkerer in you:

You'll need a supply of natural gas (not yourself, silly, but a 5-gal
bottle), a plat-cat heating element, a steel box, two 8cm PC fans, some
insulated tubing, wiring,  and a used intercooler from an older turbocharged
car.  Put the intercooler inside the box where the heating element will heat
the air in the box and transfer that heat to the intercooler.  The
intercooler inlet and the outlet will have to be outside of the steel box,
of course.   Put a PC fan on the inlet side and one on the outlet side.
Mount a tube that will transfer heated air to the PC fan on the outlet side.
Mount the outlet of the tube to a flat panel that would fit in the sliding
window opening of your westy.  Suficiently insulate the steel box, wire the
thing up, and you have warm air without the CO2 emmisions or moisture.  You
could use wound copper tubing, lots of it, as the heat exchanger.  You could
shield the heater element for more effectiveness and play with box size to
see what works best.

Anyway, it's a start.  Use your imagination.

Chris S.,

'85 Westy.