Geoff,
I'm sure either the resistors of the fan could be made to work, but hopefully some people with more experience with Newts will comment. When I had a newt years ago I just suffered any dew...
I didn't have any real dew solutions.
I would probably tend towards a 12V hair drier to clear the secondary as required rather than fixed resistors that may introduce convection currents to the optical path or a fan that might vibrate the scope. It depends how much you want to push your optics to the limit.
I'm sure there's plenty of Newt owners here who can give good advice though!
Al.