One more thing to consider here is:  is this ultimate goal heat
source to be used ONLY while stationary, or also while driving?  If
only the former, I'm going to suggest something I've suggested
before (which I've taken some flack on in the pst  :).  That is
something used on boats - a tiny, wall-mounted wood stove.  Don't
laugh:  it burns little teeny scraps of wood.  Is made by Newport.
I have friends who use it on their live-aboard boat, and they
told me it is quite effective.  You'll have to "chop" your own
wood, however  :)

At any rate, this Newport stove is carried in the famous West Marine
catalog.  If I had wall space in my '81 westy to mount it, I'd 
do it in a second.

/martha