Years ago there was a product that was a sand box with a shelf fitted on top of the sand (I think that was made by Bright Star, as bdp 24 mentions). I used a pair under my Jadis amplifiers, they were effective at isolating the amps from floor vibrations. I used play sand. Seems to me you could make one pretty easily and inexpensively too. Bdp24's advice is sound, wish I had used silica sand, as the play sand did get a little damp.
In the sand box
I have 2 audio buddies who have built component sandboxes with different types of sand. They claim Beach sand is the most dense and made a huge difference when the turntable and amp were set in them. Has anyone else been down this road? I mean there are several ways to isolate equipment, this is just one of many.