Solidstate amps don't need those
Seriously:
Placement is important - don't let backwaves slap the tube envelopes.
Brass or delrin cones are a good first step.
Sorbothane pads are helpful (Dr. Scholl's gel insoles for your gear)
Heavy and "dead" is good and dissimilar materials in a sandwich is good for decoupling.
My tube gear rests on an isolation sandwich of 1/8 in luan + Styroboard + foam rubber + 1/8 in luan.
It comes up at about 2 inches thick and is covered with an "Aunt Greta Doiley".
The old table scarf looks appropriate with a tube amp.