I have greatly reduced the 6V6 tubes' microphonics by adding these high temperature silicone rubber o-rings. There are places on line that sell the exact same "damping" rings for $5 each. I got these from McMaster-Carr... package of 10 for $6.69
The last safety step is of course a bottom cover to keep anyone's fingers away from lethal voltages. I don't have a picture of my bottom cover yet (sorry) but this project has one for sure.
On a side note one could argue that a top cage to keep kids' fingers away from the blistering hot tubes is absolutely necessary. I won't say that it isn't, but while a burnt finger hurts really bad, it will heal. A lethal electrical shock is, well, lethal. If you build something like this and have little visitors over... you decide