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Hey Keith,
Interesting plan of attack, so many fans, have you noticed any vibration?
I have a single fan at the back of the 20" primary, I find that I get a tiny bit of vibration when its on, it mushes up the image so I dont really observe with it on.
I have a thermometer to tell me the primary temperature and another for ambient.
I'm gonna install a variable speed fan for sweeping across the front of the primary, speed adjustable at the eyepiece location to set optimum speed for removing the boundary layer. Youre gonna get boundary layer issues no matter what kind of newt you use.
have a look at
www.fpi-protostar.com/bgreer/fanselect.htm
and
www.pha.jhu.edu/~atolea/WAS/thermal_management_newtonians.pdf

Setting the mirror heater to an auto thermostat setting might not be best, the dew point temperature isnt necessarily directly below ambient, it can be a few degress less depending on relative humidity.

Also, I have found that heating the primary is not the panacea you might think it is.
At around 3-4 in the morning on a dewy night, my primary does start to condensate, 10 mins with the heater on fixes that, but there is no way you can do any observing with it on, the view is reduced to a tasco like image quality, and over heating the primary only makes things worse as now it has to cool down. I generally leave it on till the dew is gone. I wouldnt use a thermostat for deciding this for you. I use the kendrick eyepeice box heater pad for this, it gives out 10 watts of heat.
One night after I set up the scope, I couldn't figure out why the view of the trapezium was barely resolvable and was getting worse!, it had me worried for a small while until I realised I had the damned mirror heater turned on, dooooh!!

No problems with fan vibration so far and don't expect any with the new fans as I have/will have them mounted with sorbithane rubber PC fan mount thingies used in the PC arena for their fan sound/vibration dampening qualities.

You've misunderstood my previous post. My Dewbuster Dew Controller as well as 6 or 7 PWM regular Dew heater outputs, 3v GLP power output and 4 12v power outputs also has a single Temperature Sensor controlled Dew heater output usually used for Newtonian secondary Dew heaters or SCT corrector plate heaters. I had installed a Kendrick Secondary heater and was utilising the Temp sensor and its output for this purpose.(ie the purpoes it was designed for. I then remembered that with my long Dewshield on my UTA and prevailing dew conditions here, that my secondary never dewed up, certainly not on my old XT12i with similar Dewshield used in the same locations.

Had I wasted money on a Kendrick Secondary Dewheater and the Temp Sensor controlled output option fitted to my Dewbuster? Turns out NO to both questions. I could re-purpose the temperature sensor and temp sensor heater output of the Dewbuster. This does not mean I lose my Secondary Dewheater either. Its just that now I will connect the secondary heater directly to a switched 9v battery mounted on the stalk to clear the dew in 15 or 20 minutes on those uber rare occasions that it might Dew up. I realised, I am not in Florida with 100% humidity, don't need a permanently running secondary heater with temp sensor to minimise heat plumes from the secondary etc etc

The re-purposing is as follows. Its all electricity coming out of the Dewbuster. The Dewbuster doesn't care if that electricity is used to generate heat in a Dewstrap, turn a motor in a servocat or indeed spin a fan. The method the Dewbuster uses to modulate the heat output of Dew straps etc is Pulse Width Modulation (PWM) which is what modern PC fan controllers use to control the speed of fans. PWM is better than Voltage regulators because no power is wasted as heat. PWM sends the full 12v just in bursts. So the Heat/Fan speed is modulated by the proportional ON/OFF time not by reducing the voltage. In other words the Temperature sensor controlled heater output of the Dewbuster can just as easily drive fans as it can power a Dew heater. I will need to wire a capacitor into the fan cable to smooth out the pulses of the PWM controller in the Dewbuster as the Pulse width frequency is low by fan controller standards which make for an annoying whining of the fan motor.

So if all I did was power the fans off the Temp Seonsor controlled heater output I would already have the means to adjust fan speed to minimise vibration with the 'Heater' dial on the front of the Dewbuster. Then I realised I could go all the way and automate it by modding and utilising the Temperature sensor itself. (Confirmed by Ron Keating of Dewbuster) Wired as it is now, unmodded and used for its original secondary heater purpose the temperature sensor tells the dewbuster to power up the secondary Dewheater when the secondary temperature drops a set amount below ambient. Obviously I do not need to worry about Dew on the primary. I don't want to keep the primary above ambient, I want to get it at or below ambient!! With the temp sensor now mounted to my Primary and inside the OTA, by reversing the wiring in the Temperature Sensor cable it will now tell the dewbuster to power up the fans when the mirror is above ambient, will automatically slow down the fans as the mirror gets close to ambient and will power off the fans when the mirror reaches ambient. Mirror at or below ambient means no Boundary layer. No boundary layer means fans can by slowed/powered down to save power.

Like so many mods to my scope, they might be complicated in installation/wiring etc but are aimed at making the scope as easy to setup and use as possible while maintaining a high level of functionality. This particular mod combined with the fans is all about making best use of limited observing time/windows/suckerholes. I don't want to wait for hours for the primary to cool to ambient and for the boundary to disapate naturally. I want the mirror to deliver its best from the getgo. Nor do I want to be fiddling with fan speeds all night, wondering have I turned them off too early, is this crap atmospheric seeing or is my mirror still not fully cooled yet etc. Automate it and forget about it is my motto It never ceases to amaze me how versatile the Dewsbuter controller is.

ah, ok, I get you now.
Sounds grand, telescope modifying is a hobby all on its own.
I've made so many mods to the UTA that its alot heavier then it used to be, so much so that I'll have to put some weights (about 8kgs) on the LTA to balance it.
I've got to the point of having to put the UTA of the scope out of sight as it was coming to the stage where I'd never stop modifying it