Well, not being familiar with your conditions I can only say that my Telrad is essential for my observing and is protected at all costs. I have made a dew shield that is simply a piece of cardboard that is velcroed in a loop over the whole length of the Telrad. This protects the finder from falling dew and is very simple and cheap to make.
I'm sure that the commercial heaters and shields are probably better but not for the cost
