Tubes, to damp or not to damp?

O-rings are too tight and apply pressure on the glass.

Only if your a total (whatever) and purchase them too small.
here there are sizes that vary in just 1mm ID diameters, from 4mm to 61mm ID (inside diameter) with 2mm thickness to suit every tube you have, on this site. Others have them up to 85mm ID
Just measure your tube diameter and go 1mm less for a neat fit without being tight!!!!
https://www.ebay.com/itm/2mm-Cross-Section-OD-8-65mm-FOOD-GRADE-Red-Silicone-O-rings-Washers-50-100pcs/193009581470?var=493208405430&hash=item2cf0447d9e:g:sOcAAOSwKTddNtGK

Cheers George

silicon or rubber is a no for two reasons, the crack over time due to heat and loose their grip and overdamp but are cheap.

Sorry you’ve got that wrong the red silicon are very high temperature industrial silicon rubber, made for extreme temps and don’t stretch or crack over time. The black ones are not high temp and may sag.

Cheers George

Don't spend a fortune on audiophile o ring dampers, get these a couple of dollars.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Red+silicon+o+rings&_sacat=0
But not too tight as over time they will dent the glass with the heat.

Cheers George