A couple of comments:
In Westies, the regulator is connected directly to the
service valve (on/off valve.)  The original regulator
(square diaphrams) had a box to protect it.  New regulators
have the white plastic cover, so that box is not needed.

The vents MUST point DOWN.  This is important.  There are
regulators where stage one and stage two point different
ways--do not use them!  The whole point of a vent is to
let any condensation drip out--so it must point down.
The cover is to protect the vent.  The Westies (and
apparently the ASIs) have a bash plate or guard, which
protects the valves, regulator, etc, from gravel, etc,
and also adds protection to the vents beyond the covers.

Here, for example, is a regulator that you do NOT want to install
on a horizontal tank:
http://www.campingworld.com/browse/skus/index.cfm?skunum=26059
because when installed horizontally, the vents will not point down.

Richard
Boulder