I would support Martin on the benefits of aluminium foil – I use strips of insulating foil from a well known DIY store at the business end of my 200 mm Newt and various refractors in addition to a dew heater strap at the front of all when in use. For my 14inch SCT two dew heater straps – one at the corector plate end set at full power and at half power at the mirror end. Combination of dew shield with aluminium foil keeps the exposed end free of frost or dew and the half power dew heater keeps the mirror clear in use. When parked it is in a wooden observatory and the dehumidifier is switched on and not had any droplets on the mirror.
Peter