If you're using compliant feet like Tenderfeet or Iso-Cups between the amp and platform, Extra-Thick
grungebuster Dots between the platform and floor will in most cases provide more than adequate isolation/decoupling.
If you're using the factory feet or rigid coupling devices like cones under the amp, it's hard to say, with so many possible variables involved in the vibrational environment.
Tenderfeet are usually used under the component instead of under the platform, but they usually do very well under platforms also.
Steve
Herbie's Audio Lab