I've only dewed up once in Brissy - and it was 3am towards end of winter. Low tech solution has been working since then - a thin piece of camping foam formed into a 12" cylinder I pop on the end of the scope. If you block "line of sight" between an object and the heavens its a lot harder for IR energy to escape such that object (2ndary) is cold enough to dew.
p.s. Most Brissy folk worry they're going to freeze to death below 10 degrees celsius....
