I doubt that burying your amps in sand will do anything positive and will almost certainly have long-term negative effects. If you are concerned about the housing of your amp vibrating, or responding harmonically to soundwaves, then you might try the VPI "Magic Brick", which was "invented" to address exactly these problems.
Would sand help my amp?
Seeing a recent thread on sand-filled speaker wires got me to thinking. Would burying my amplifier in a tub of sand reduce or eliminate any potential harmonic disturbances? I don't *think* that the sand would do anything to hurt the amp (power amp, no moving parts), and it just might clean up this slight tizziness I hear at high volumes. What do you A'goners think? Has anybody tried anything like this?