Vibration Control for Lightweight Tube Components

I'm looking for suggestions to isolate a lightweight tube preamp from vibration and resonance. Not acoustic vibration, but physical vibration from the stereo rack. When I touch the shelf the preamp sits upon, the sound can be heard thru the speakers.

I am using a heavy furniture grade stereo rack for my components, all using Herbie's Tenderfeet for isolation, including my TT. The preamp only weighs 7 lbs. and has Herbie's tube dampers applied, but needs to be decoupled from the heavy wood shelf. I've tried the Tenderfeet and Vibrapods under the preamp, but neither provided isolation from vibration.

So, what are owners of lightweight tube preamps and amps using for vibration control? (there is a limited amount of space between the shelves).