Keep in mind that a tube buffer is not the most problem prone device when dealing with tube gear. The top honor requiring the greatest freedom from noises extraneous,or inherent to the tube itself go to high gain stages in the phono stages and active preamps.
Keeping the internal circuitry of your tubes isolated from vibration is almost always good for your sound. One day you too will find a micophonic tube so don't let a "friend" use the pencil-eraser/hammer test to elicit sound from an operating tube. ( I might add for humor you should really avoid any traumatic physical force applied to the outside of tube, except if you are testing the truth about the cold war nonex glass (Red Bank Bendix) capable of enduring some but not extreme enviromental issues)
Thus while the tube itself which is most often thought of as the focus of attention, apperently rightly so, with the prevailing attitude being that there is something vibrating within the tube, or against its envelope, which yields a ringing sound, it is not the only approach. Given your woodworking skills you might for the heck of it try it on your audio.
Dampening the vibration of the Tube Buffer chasis might help. The trick is to "drain" the vibrations onto another substrate, thus note the use of pointy brass cones for feet. The recieving end of the points and the weight of the cones should dampen the chasis itself. A good way to further the cause, is to float the receiving board as in a sandbox.This provides highly effective vibration dampening preventing the vibrations from transmitting back up into the buffer's chasis. Plain tube dampening rings are IMHO not very effective (I cannot comment on the Herbies versions). The best I have are heavier and they are made of metal which may hold in or dissipate heat which in turn is presumed to have an impact on the tube's longevity.
If it is a 6SN7 buffer chances are high if old stock and an early production tubes are in it will be microphonic. The good news for you is that microphonics sound bad to most ears if it is currently present and since you aren't sure you need isolation you probably don't have a case worth the cure.
OTOH if you can build a sand box and want to buy some tube rings you may not know what your missing. I knew what I had, because in the gain stage of my pre amp I use 6SN7 GTs 50-60+ years old mostly. I felt at first I had wandered into a belfry.
