I believe that the reason for not using the propane while driving is
that it is UNSAFE to do so. If there is an accident, the van may go up
in a fireball due to leaking propane. Also, there are problems with the
shutoff valve leaking around the stem. The valve is not designed to be
subjected to road vibration while it is in the open position. The mass
of the valve stem and its handle might damage the seal if there was
enough prolonged movement.
Mark Drillock
87 Syncro self westied