Natasha benefits from the four generations of active cooling/fan configurations I have used on Frankenscope over the years.  (Hey, part of Frank's name comes from the fact that it is a test bed platform for experimentation!)

Natasha features SEVEN low vibration personal computer fans, all but one (the main intake fan) variable-speed controlled via potentiometers/rheostats.

1.  I installed a low vibration (German "Noiseblocker") 120mm fan mounted behind the tailgate to pull air in around the back of the primary.  This is reputed to be one of the most low vibration fans on the market (albeit at the cost of reduced air flow), and I therefore didn't bother to make it variable speed.

2.  Since the aggressively sized dust cover in the mirror box is a scant half inch larger than the primary, there is little chance for this air the 120mm fan is pulling in to vent freely, hence an array of fans was installed on the back side of the mirror box, above the mirror and below the internal dust cover.  Since this is the part of the mirror box that will usually be highest (unless the scope is pointed at zenith), hot air should rise to this edge.  The array of four 80mm fans-- a mix of "Noiseblockers" and Panasonic "Panaflo" models (also touted for their low vibration and the especially broad arc formed by the air flow) were spaced to cover the full width of the interior of the mirror box.  (Note that light intrusion through these vent holes would be an issue under suburban skies, so look at the light baffling page for details on my solution! Light baffling)

3.  Two other 80mm Panaflos were installed in the opposite corners of the mirror box, angled in to produce a good laminar flow across the mirror.  These fans are pushing the air brought in by the 120mm fan, and hence have no dedicated air intake holes.

All of these fans were commercial models reputed to be among the quietest on the market-- and low noise usually translates into low vibration.   Despite this low intrinsic vibration, I took great pains to isolate each fan mechanically from the structure of the scope.  Each is mounted to the scope by elastic bands, not screws, and each point that comes into contact with the scope has a sandwich of two types of closed cell foam (one Sorbethane/shoe insert type, the other mousepad-grade) between the fan and the wood.  I think I went overboard here!   :-)

I had two older model 80mm fans lying around (I've been building my own personal computers for 20 years) and decided to put them to use in cooling the FRONT of the primary mirror prior to observing.  I took some scrap plywood and made a second mirror cover--not as nice as the main one or as dust tight, since it will only be put in place during scope set up and run to directly cool the coated side of the mirror.  The two fans are installed to blow filtered air down onto the mirror.  I let it run one summer's night of relatively stable air temperatures for a full two hours prior to observing, and was rewarded with my best planetary views through the scope yet!  Having a thin primary-- 1 3/8" thickness-- helps it reach thermal equilibrium, too.

120mm fan attached to tailgate to pull air into mirror box and around primary mirror

Exhaust fan holes in side of mirror box.  Note the eyelets that will secure the elastic holding the fans in place.

View of the six 80mm fans in place.  Note the elastic holding each fan in place, and the rubber cushioning.  The four fans to the right draw air out of the mirror box (the light vent is lying "open" in the horizontal position to the right of the fans). The two fans at the left are angled to blow air across the mirror and maximize the laminar airflow.  The right and left set of fans are each variable speed and controlled by a separate potentiometer

Painting one type of rubber vibration cushioning flat black.  Notice the pieces of rubber installed as "feet" on each of the 80mm fans at right

Top side of my improved "mirror face cooler" showing the furnace filter material placed behind the intake holes for the two fans.  I wouldn't want to blow dust particles directly onto the mirror face, even though these are relatively low velocity fans!