Thanks Peter, the Photo.net thread was very useful.
I'm a bit paranoid about ensuring slides are dry before mounting under glass as I had a couple of nasty experiences when I first started using slide film. I hated the cheap and nasty Kodachrome cardboard mounts with their fuzzy edges, so I used to transfer my "keepers" into GePe anti-newtons. My old house didn't have double glazing or central heating and, unbeknown to me, was perpetually slightly damp. The inevitable happened and, like you, I learned the hard way.
Where we live now is as warm and dry as King Tut's sandals - so no fear about storage. In any event, I'll be scanning the negs to very large TIFF files so, if the worst happens, I'll still have a very usable image. Not the same as a negative but still worth having.
Regards, Paul.