How to keep back window from misting up

[GGill]

Hi - my car is awash with gadgets, sponges, kitchen roll - all to try and keep my back plastic window from misting up in the winter.  It's extremely badly scratched anyway, and I'm virtually driving blind from a rear view point of view at the best of times....without having it mist up too.  I've just bought a de-humidifier bag from Halfords, and that's filled up with water over night - but the anti fog wipes I bought are absolutely useless.  Didn't help at all.  Ideally I'd like a new plastic window - but the fitting would cost an absolute bomb I've heard - even if from an old StreetKa spares dealer - I've heard the fitting of a new window or roof is very time consuming.

Has anyone got any suggestions as to how to try and keep the back window from misting up?  I find myself having to pull over every 5 minutes when it's really bad, despite having the heater on, and window slightly open.

[TomsFocus]

Are any of your carpets damp?  Usually when windows keep fogging up like that it's because there's water inside the car.  With a cabriolet I'd suspect a roof leak.  If you stop the leak, the windows should stay much drier!