The only concern I would have would be thermal currents within the tube caused by the warm mirror vs the outside temperature.
I wonder if it would not be better to modify the scope in such a way that you had fans moving air across the face of the primary.. This may well increase the ingress of dew, as outside air would be damp and blowing it onto the mirror would cool the mirror, making it more susceptible to dew..
Another thought...
Wouldn't having rear fans on the ota, blowing air into the tube (provided the rear end of the tube was sealed apart from the openings for the fans) help by pushing airflow up the OTA, stopping moisture from entering the tube...
These are all things that I considered with my 8" RC. as its primary mirror was prone to excessive dewing due to its short tube and relatively small mirror. The thoughts on thermal currents were highlighted to me by Paul Haese, As I was considering a dew heater for the secondary mirror. His testing had shown him that use of heaters on his SCT when planetary imaging had a detrimental affect to image quality. Obviously, for his setup, when imaging the planets at 8000~14000mm focal length, these affects would have been heavily magnified. Still I wonder how much of an affect it would have if you were taking very long exposures at short focal lengths (700~900mm) vs very short exposures at very long focal lengths..
I suppose there is only one way to find out...
Ps.. What's all this about Newtonians? Don't tell me you've been pulled down the aperture of a big fast newt again!
(I'm working ever so slowly on something rather similar myself..)