I feel everyone here is overreacting to a minimal problem.
Think of this;
Boat batteries are in the engine compartment where there is heat, &
spark.
The batteries are vented, right into the engine compartment, and I have
never heard of an explosion, or any other problems because of the gasses
expelled by the batteries.
A battery will only give off mass dosses of gas when put into a
overcharge situation.
Like at a fast charging rate of 80 to 100 amps off a battery charger,
continuous.
I don't think a Vanagon will put out that kind of amps continuous for
long enough to cause any mass explosive gasses to accumulate inside, to
cause an explosion.

Terry,

85 GL