I agree that it would be ideal to have the wind gen be able to rotate 360 degrees. I don't really like the idea of the top of the mizzen mast because it would require removing a TV antenna and fabricating a piece on the top of the mast to make it flat. It is also more difficult to install and service and puts more stress on the rig.
I found one custom design mount that allows 360 degrees of rotation on the front of the mizzen mast. (photo below)
There are only two photos of commercially available mounts that I could find. One is the vibrating isolating mount from SV hotwire (makers of the the KISS.)
The other is from Emarineinc.com.
There is another mount sold by hamiltonferris, but I don't know the specs on it.
The KISS mount doesn't allow 360 degree rotation, but it would be nice to reduce the vibration in the rig. It is also the least expensive option.
The Emarine mount does allow complete rotation, but it doesn't look as robust and it is much more expensive.
Still looking for that perfect mount that will allow 360 degree rotation on the front of the mizzen mast and someone that has seen it in action.