Something which worked well for us back in the day was to get a 10 foot long cast iron pipe, complete with drilled flanges at each end, from a scrap yard. It was painted inside and out with bituminous paint. A hole of suitable dimensions was dug so that a plug of concrete 3 feet thick and three in diameter could hold the bottom of the pipe, which was buried to slightly more than half its length. The inside of the pipe was then filled with sand. The top flange was ideal for attaching an equatorial head.
The fundamental vibration mode and small harmonics were heavily damped by the concrete and through being clamped with back-filled sand. The internal sand quenched high frequency vibrations very effectively.
It was possible to have one person placing fingertips very gently on one side of the pipe while another hit it as hard as possible with a length of 2×3 on the opposite side and still feel no vibrations.