the clear film could be applied when the weather starts to turn cold and left fitted..
the blanket could be thrown over when you go out first thing an left on while you go inside for breakfast or a cup of coffee..
the other option ( and one I saw a bloke do once ) is a gas blowtorch with a wide flame nozel...
or a stick on heated window? ( another great idea for dragons den.. a clear film with a heated window wire in it that you stick to the windscreen.. either hardwired or on a cigarette plug.. )