Alex,
There are two solutions I'm aware of.
The first is vibration pads -
http://www.bhphotovideo.com/bnh/cont...=REG&A=details
The second is tricky and utterly counterintuitive. Basically... a telescope and mount has a resonant fundamental frequency and harmonics. Vibrations close to this will incite oscillations at the fundamental and harmonic frequencies. To stop these there is another choice.
This involves lowering the fundamental frequency so that it is much LOWER than to the exciting frequencies in the noise (coming from vehicles via the ground).
Stiffening the mount often fails - actually makes it worse - in that the stiffer it becomes, the better it is able to track the driving frequency of the noise.
The solution is to perch the scope on a "sloppy" mount that cannot respond to high frequencies, yet is stiff enough to use. The example I am aware of is an 8" f/7 Newtonian mounted on a tall pole (10cm diameter steel pipe, 4 metres long) to get above a house and surrounding trees. The pipe was filled with a viscous oil and it had a sway damper attached near the top to the house, I don't know what this was exactly but probably similar to a shock absorber. The owner was mechanical engineer, BTW.
Steady as you could wish, and didn't respond to vehicles passing. If you pushed it, yes it would sway a bit but always came back to its original position.
For your C8, this would be like mounting it on about a 1 cm diameter pipe, 1 metre long, set in a concrete block with something to damp the motion. Yes it will move a bit if you nudge it or in a breeze, but keep your mitts off.
In vehicles there is a similar analogy - airbag suspensions, used in the Millennium and Waratah train and buses, and also used by Mercedes. These are utterly unlike conventional springs in that they have a very low fundamental frequency, far lower than can be achieved by coil springs - and results in the "magic carpet" ride these vehicles have, utterly immune to the dreadful lumps and bumps in the track below - as a Tangara passenger will feel.