and even the hottest-running ones won't foobar that.... "shock-absorb" tubes, which is always an issue when doing high-volume gigs (raves and the like).
That could work. Some things to address;
Heat dissipation. As well as being resistant to high temp, it also insulates very well, so you would have an issue with the tubes being able to dissipate heat.
It's also very adherent, so changing tubes would be an issue.
Though as I write that, I can see making a tight-fitting collar around the base of the tube.
Shape a circular piece of plastic about 2cm tall about 4 mm in radius wider than the tube socket, affix it to the board. That will have the rubber go maybe 1/4 of the way up the tube sides, which should leave plenty of glass surface area for heat loss.
Put a dummy/old/dead tube in the socket. Pour the rubber mixture inside the plastic circle, it would adhere to the board and the base of the tube. Pull out the dummy tube (which would be a chore), then put the working tube into the tight collar of rubber.
Lots of shock cushioning and very unlikely to work loose.
Since I haven't gigged live in waaaayyyy more decades than I care to admit, not useful for me, but someone might want to give it a try.