The fresh air for a vanagon motor comes down the right side of the van and enters the air cleaner in a space separated from the actual engine bay.  How would CO2 in the engine bay kill the motor?  Just wondering?
George 
'85 westfalia

They make systems like this for boats, and I seem to recall one company
adapting one to sell to motorhome owners. The boat ones often have
automatic trip mechanisms, but that's not recommended for a van because
the CO2 will instantly kill the engine.  Not good if you're in the middle
of a passing maneuver when it goes off!