Does anyone sell a "sandbox" type isolation base?  I'd like to try one out but can't find one to buy on the internet.   I suppose  a local cabinet shop to make one out of MDF or Corian.

I have had several of these built in the past for professional applications.  I know of nothing more effective for isolation short of pouring a support as part of a concrete floor (which was done in the old days of radio). 

However, I recommend water washed gravel over sand.  It has less change of finding its way out, and is much easier to deal when you need to lighten the stand for transport or moving.

Also, with a bit of luck you may find a commerical lamp stand or display stand of the right height that either can be strengthened or is already stout enough to handle the load. 

Dave