> I've put a piece of 2x4 under the bottles with no problems.
>
> Ed

Ditto. I used to use a can of water chestnuts as a shim (it was the
perfect size), but after several years of pressure exerted by the
bottles the top weakened and caved it. It was quite a mess....

Jack Keller, The Winemaking Home Page
http://winemaking.jackkeller.net/