Looking for a water resistant 'sandbag'

["Ad Sach Singh" <adsach@zzzzzzzzzzzzzz>]

Hello stone list,
As the spring watering season has begun in Boston, I discovered that my landlord has arranged the sprinklers for about 15 seconds of watering to occur INSIDE my carving gazebo. I personally find this refreshing to the skin and except for a banker I left out one day my tools seem to be fine. My problem is that it has started to mold my canvas sandbag where it contacts my carving table.

Currently I am carving Marble in the 80-200 lb range. I like to reposition the sculpture for multiple carving angles using a sandbag and Lazy Susan (once I have lightened the stone by a few gallons of dust.) Does anyone have an suggestion for a water resistant sandbag?

- ad sach

P.S. I am resistant to the idea of a screen, as I enjoy the 'plein air' carving experience.

P.P.S. My wife suggested a silicon filled bag. While it might be fun to carve upon a DDD breast implant, I imagine that would be cost prohibitive and probably a bit too fragile.