Peter, you might be surprised but with altitude and cool winter air it may well stay dew free for longer than you expect, these scopes have an undeserved reputation IMO. I have frequently used my C8 in the Blue Mountains with neither. Other times, and closer to the coast, it needs both
If you buy a heater strap you'll also need a controller / means of controlling the current to the heater strap, otherwise you could be overheating the scope and cause tube currents.