@audiozenology, the only rubber I use for isolation is a set of Sims Navcom Silencers in place of the stock springs in my VPI HW-19 Mk.3 turntable, a favorite mod amongst HW-19 owners. While the stock springs provide the well-known isolation inherent in suspended subchassis tables, they allow a fair amount of relative motion between the subchassis (containing the platter and arm/cartridge) and the base-mounted motor.
The EAR Isodamp I use is not the constrained-layer damping model (C-1002), but the version made for the damping of vibrating/ringing metal panels and chassis (SD125). It is a heavy (about 1lb. per square foot), dense, stiff, 1/8" thick material with adhesive on one side. Applied to the metal chassis of hi-fi electronics, it is very effective at absorbing and dissipating their ringing resonances. Unless you consider electronics to be musical instruments---a silly notion imo---and should therefore be allowed to ring away, a very effective solution for eliminating unwanted resonances. While my phono amp, linestage, and power amps benefit from SD125, my very robustly built Esoteric digital player has no need for it---that 47 lb. box is very well self-damped. I guess I can't be a card-carrying member of the low-mass-is-a-gas gang, ay? ;-)