Also, try to avoid large plastic spinners. They're usually mounted far away from the motor and any small run out (bend away from straight) will make the spinner "wobble" and that is a huge source of vibration. The "Hyperflo" fans from Great Planes are notorious for this trait. If at all possible avoid spinners, or seek small aluminm ones, or small spinner nuts.

Let us know how you make out. I'm curious which fan you're using.