Garmin Zümo 220 severe rain cover

The Garmin Zümo 220 is a waterproof motorbike navigation system, but how "waterproof" is that? On August 17th, while riding in Germany, the poor Zümo got so much water thrown at it, that it's mini-USB connector got wet... Which then resulted in malfunctioning due to the short-cut on the connector.

In defense of the Zümo... the weather was utterly horrible. All day. :-)

Anyway, riding without navigation in the rain isn't my thing... So, I figured to have a go at constructing a rain cover