We are often asked if we sell 'blank' windows to use as a black out panel for the rear panel on the driver's side of a Campervan conversion. In reality such a thing does not exist- the trick is to use a normal rear quarter glass and somehow black out the metal underneath. If you have a dark coloured van there's no issue but with a white or silver colour you will be able to see through the glass and detect the metal beneath. 

2 options - paint the metalwork beneath. Apply black vinyl to the body work or apply vinyl to the back of the glass.  

The last option is not a good one as you'll almost certainly get bubbles appearing in the vinyl and they will be visible. 

What about condensation or air expansion in the sealed off area?

A valid point. We suggest simply leaving a small gap at the bottom edge of the window when applying your adhesive bead.