There is another consideration with dewing. The other night, while waiting for the clouds to clear
) a few of us were discussing the issue of dewing in newtonians. Someone whos name I've forgotten (sorry mate - too many new names) reckoned that you have far less trouble if the tube is silver or white. It's to do with the loss of heat - black is a very good radiator of heat while white is very poor. So the light coloured scope will stay a bit warmer. I also read the same thing in S&T years ago.
This seems to tally with my experiences. My newt is white and is pretty dew-resistant (the decent length of tube in front of the secondry helps too). But the black refractor gets a layer of dew over it at the drop of a hat.
The S&T article I read also gave me the idea for a modification I made to some 15x80 binos I use in an observing chair. These dew up almost anytime. Cardboard dew caps helped a bit. I made new caps out of heavy aluminium foil, reenforced at each end and painted matt black on the inside. Then I wrapped the body in that silvered flexible material they use in house insulation. The improvement was dramatic. Now they only fog on very bad nights if I look too close to the zenith
and for then I have a 12V drier.
I know this approach won't stop a SCT from dewing and you will need a heater. But others may also find they can control their dew problems passively.