Please allow me to introduce a project of mine.
Since I wasn't able to find a solution (maybe there is now) for controlling a 12V fans I made my own circuit. Now, after 2 years and zero problems using 10 units running 24/7 a feel confident to offer it to the others.
I made a website just to evaluate if there is an interest big enough for me to make a batch production.
If you are interested, please submit the survey form at the bottom of the page.