Today, using spacers underneath part B and large washers underneath part C,
I extended the distance between those parts and the rest of the vent by
1/4", thus allowing increased airflow on the intake side.  See drawing at
http://www.takingflight.net/images/fluevent.pdf

This had the immediate result of allowing the fridge to light first time
with very little pumping and stay lit, thus resolving my problem.  I don't
know yet if it will stay lit while driving, but either way, it's a huge
gain.

Paul