Thanks David,
I will give all your points due consideration--especially the resonance
factor.  As for "green water"--I am sure I can cap the thing off.
But as to snow/ice dams!!!
When this CA girl finds December's overnite lows dipping into
the low forties, she tosses snorkle gear in Westy & heads
south.  Why do you think the goddess gave us Vanagons, if
not so we could throw all out stuff in the back & move somewhere
else!

> As to the weight, it may very well not be a factor.  However, it should be
> borne in mind that these units are normally installed on surfaces that
> expect to have people walking on them, not on thin resonant panels where
> they would act to drastically lower the resonant frequency of the panel --
> and the shock/vibration regime in a Westy is considerably different than a
> sailboat.  This may not be an actual issue...but it might.
>
>
> >And properly installed, allowing for differences between a
> >Westy's fiberglass roof & the normal installation of these units
> >on sailboat cabin tops, I can't see why they would leak!  They
>
> If you take green water over the roof there will surely be a deluge
> <g>.  These vents are not meant to be used in heavy weather underway, they
> are to help keep the cabin dry when the boat is closed up.  Bearing in
mind
> that ordinary driving in a Westy amounts to a near-hurricane in a
sailboat,
> I would expect possible issues with noise and possibly unwanted inflow
> depending on the pressure zone where the vent is installed.
>
> Thought needs also to be given to the possibility of snow/ice dams -- I've
> experienced leaks through the regular skylight from this cause.
>
> Of course all of the above is avoided by removing the vent and
substituting
> a blank deck plate when under way and during snow season....
>
> david
> David Beierl - Providence, RI
>   http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage"
> '85 GL "Poor Relation"
>