Just like the bathroom until a window is opened, if the air space in the instruments is sealed, the "window" will mist up.
If you can remove a light fitting to allow air to circulate, you may find the misting clears.
Whether you can introduce another air inlet and keep the lights, I don`t know. it`s not an area I`ve accessed on my`04.
Ray.
PS, is water getting in from on top at all? that would help to cause misting.