Hi, peter I know exactly what you are saying, when I was imaging, I too had a 3x3 meter roll off Observatory! it worked a treat an at times dew was a problem.
I did use 2x30-centimeter fans and the air flow really made a difference, and it had absolutely no effect on imaging.
I actually kept these fans running full time, even when I had finished imaging and during that time the air flow also dried out any equipment inside the observatory as well, when it was closed.
The fans ran 24/7 all year, hardly used any power and when they wore out, I replaced them with a new one from B W for 15 bucks.
It does make a difference, just have them on a stand or something similar and not to close to your equipment and just on low, let the breeze gently pass over, it really works a treat once you have them in the right position.
Just one thing though, don't cap your scope until all is dry.
Leon
