Mark McCulley says:
Many of the standard propane regulator are adjustable, but I
don't know
what their range of adjustment is. A good propane supplier
should be
able to answer this question. These types of regulators are
not designed
to be installed in enclosed spaces however. I would
recommend installing
the regulator outside the van as they can suddenly vent
blasts of
propane.

I've had occasion to maintain, service, install plenty of
rebuilt kits etc. on
regulators for businesses I owned.   These were not propane
systems, but
some things are the same.  If I need two pressure levels
downstream from
the high pressure volatile liquid tanks, I'll set the
primary regulator for the
higher value and feed my second in-line regulator from the
first.  In the
case of propane, I would certainly want my primary regulator
outside, but
I would feel perfectly comfortable in having any downstream
regulators
inside my Westy.   After all, it's highest working pressure
will already be
regulated down by the primary regulator.  Keep it simple.
Plenty of end
devices contain a final regulator anyway.
John