My scope is mildly odd in that the only optical surface exposed to the sky is a plane parallel disk of glass which serves two principal purposes. One is to keep dust, wee beasties, etc out of the way. The other is to support the Cassegrain secondary without introducing nasty diffraction spikes.
Dew is kept at bay by a very feeble heating element wrapped around the end of the tube and which doesn’t appear to cause any annoying air currents. Such a device could easily be used on any scope with an exposed front surface.