Just a thought;
A couple of us with heaters of various types, have fabricated/installed a
polypropeline blanket thermal barrier that snaps onto the Westy air duct
rails just below the van roof line. It makes a huge difference ... 20-30
degrees compared to the air at the canvas top level.

Bob Stevens
'87 Westy Syncro
"Passion Fruit"

Everything is installed and working.  The output is less than I had hoped
for; though it blows hot air like mad I'm thinking that I will need to
really insulate.

    After an hour of running it on high it was on the lower end of warm in
40ish degrees here in Oregon (Tuesday).  It is better than the space heater
I had, just not the heat volume I had hoped for.  Maybe I am being too
critical (it is only 6800 btu afterall)

   This weekend I am camping on the coast so it will be the real test.

   More to follow
Brian