motorhome rooflight cleaning

I have a hymervan512, the washroom rooflight is double skinned with small vents in the centre, when the rooflight is shut these vent to small openings on the underside so it vents when shut. Problem is cleaning between the two sides. Dust and muck has blown in. I don't particularly want to unclip the window from the elevating mechanism. Any ideas? Have tried coat hanger with sock etc, not ideal!