Fitting the cam to the a-frame the other weekend was really just a test, which seemed to work pretty well. In my case, the reason for the vibrations was the fact that the camera was being held in place by a plastic bracket, which raised the cam around 15cm above the a-frame itself. Holding the camera onto the a-frame directly would have solved this issue, but would have been impractical at speed.
For the past 3 years, I've taken videos by manually holding the cam - it's been ok, but isn't very easy when you're driving too - a case of point and hope for the best kind of thing. I've had a good few occasions now where an a-frame mounted cam would have been excellent.... we came back from Skomer last year through some significant swell, which was taller than the aerials on the back of the boat. Unfortunately, I was too busy trying to keep the boat surfing, and the other two guys were holding onto their diving kit which meant none of us could get any footage.
Anyhow, another mate who cycles a fair bit uses one of these -
It outputs composite video to a Sony DV camcorder which then records both the video and the audio for him. Since it's so small, I'd probably mount it on the next highest object on the frame - the radar reflector which doesn't bounce around too much. Obviously it's trial and error, but the output can be pretty good
Depending on the cost of my engine service this month, I will be seriously looking at getting this kit once the visa card has emptied a bit