Philip, no dew for certain with your set up, it is still using a heat source. I would venture to say that your rig uses less power too because of the insulation, which is a good thing though.
Markus, no vibrations. Even at 560X, no vibrations. I have a PWM unit connected to my wee 40mm 12V fan, I have never seen vibrations at any fan speed setting.
I have been using fans with my scopes for many years now (dobs longest of all), and I have never experienced vibrations.
Heat does have a place, but it is less than we think is necessary.
Where we set up our scopes is also another factor for dew control. From home we may have no choice but to deal with dew. But if you are mobile, then site selection needs more careful consideration. The dark sky site I use, I've been using it for more than 12 years. In all this time I have seen dew form only five times. The biggest issue I have there is not dew but my breath which can fog up the exposed secondary of my dobs. I could just stop breathing...