On Saturday, 7 May 2016 15:58:46 UTC+1, Bert Coules wrote:
Many thanks for the speedy replies. I was thinking of a loose tent-like
protective cover rather than completely enclosing the material with plastic,
but on reflection (and if it proves practical) perhaps the latter might be
better.

Are silica gel bags commercially available? I'll check.

Salt is far cheaper


NT