GW sells a pressure regulator with a cover.A Marshall 290,I believe.I may
have the following numbers reversed.It is not summer and this detail is
out of season.The GW catalog will clear this point up.
 The vent on the regulator needs to be pointed down.This is for the
condensation drip.Propane is a refrigerant,too. When the regulator lowers
the pressure from tank pressure , to 11 inches of water column( about 1/2
psi), the propane gets very cool.The reason propane is considered a
refrigerant, is that there is a direct relationship between the pressure
and tempature of the propane. Lower the pressure, and the temp drops.Water
will condensate in this valve area , when the pressure is reduced.It will
turn to ice and the valve will not to respond to altitude changes well, or
regulate the pressure accurately.It needs a way to drain out.It drains
throught the vent, so it must always be  be pointed down, and be clean of
road dirt. A Marshall 299 will work fine, but the vent  needs to be
pointed downward.It is the same inside as the 290, but the vent is
pointed differently, by 90 degrees.The Marshall 299 is commonly avaliable
at rec vehicle centers. Not so the 290.

The  plastic cover on the 299 protects this vent area from clogging with
road dirt.It is really the only area that needs to be protected.The 299
does not come with a cover.