I have a stainless "cover" that was fabricated by an aircraft mechanic and given to me by a list member. It is held onto the vent by a nut, which screws onto a bolt that was put through the center of the vent. Works very well and easy to remove or turn upside down to store it while using the vent if needed. The "nut" is a brass wingnut.

bob stevens
'87 Syncro Westy

 I had just about given up when I
> noticed we had a round Rubbermaid container in the cabinet in the kitchen. It
> looked about the size of the vent, so I took it out to the Westy to measure it.
>
> Its a slightly larger diameter than the metal part of the vent. However. it is
> just a touch larger than the diameter of the rubber gasket that surrounds the
> vent. It fits tightly around the rubber gasket and sits flush against the body.
> So I'll try it out and see if it blows off or stays put over the next few days.
>
>
> If you are iterested, it is a Rubbermaid "servin' saver" #2, the 1.7 pt or 850
> ml size.
>
>
> Ric