I balance my props dynamically, so they generate very little vibration. Still, nothing is perfect, and there is always the vibration caused by AERODYNAMIC unbalance that is hard to correct. Aerodynamic unbalance occurs when one blade has more lift than the other. As the blade rotates it pulls on the motor shaft in a circular motion. This twists the motor mount in a sort of "Calypso" movement and excites resonances.
The bottom line is - it is impossible to stop every vibration at every possible motor RPM.
I bought a decent gimbal on-line for about $55. It had the little black vibration dampening "balls". It also had just a flat bar for the camera to sit on. The flat bar had two slots for a strap that connected to a ring that went around the lens. The problem is - the slots were in a place that put the USB port of the GoPro against the "pitch" motor. It would be impossible to connect the camera to a video transmitter.
So I printed a different camera holder. One that wraps around the camera on 5 sides. And it leaves the USB port accessible.
I flew the gimbal, and it worked well to hold the camera level, but there was too much "Jello". I had some super-soft dampening balls that I had bought from Hobby King. I put those on the gimbal and tried again. This time there was very little wiggle in the picture.
Moral of the story: Get some very soft dampening balls of various sizes. They will come in handy.