RE:It also strikes me that two adults, a child, and a dog will convert a
large

> amount of O2 to CO just by breathing, maybe more than a small propane
> flame--I don't know.

Just by breathing we produce CO2, not CO (Carbon Dioxide vs Carbon
Monoxide).  The danger is from CO, not CO2.  CO binds with the red blood
cells and stops the absorption of oxygen into the body, CO2 is expelled,
it's what we produce.

But I believe your point is well taken on the inherent ventilation we get in
our Westfalias because of the canvas top.  The question remains though, if
there is no appreciable wind, would you get enough air exchange to keep
levels below that which becomes dangerous.  I am aware of a recent incident
in a Westfalia where the occupant had used a catalytic type heater for
several hours during the day but there had been little venting.  Even with
the heater off in the night the occupant found themselves unable to get
their breath in the middle of the night, had to open the door and get
outside.  After the van had aired out, things were fine.  The conclusion was
that the air in the Westy had been depleted of oxygen and that air not
replaced because the van had been buttoned up pretty tight.  In this case
the top was not all the way up, only propped up a foot or so.

--
Loren Busch
"I ordered a feast in the hope that you would come."
"I came in the hope there would be a feast."
(From "Monument" by Lloyd Biggle Jr.)