We have the best luck with the black plastic boxes (25 slide capacity)
with a small nylon process bag or lens paper containing silica gel to absorb
moisture when you bring sections back to room temperature.  We also
wrap tape around outside to seal box, this may be overkill, but it
provides label.  Avoid calcium chloride, anhydrous as a substitute
for silica gel, Drierite (sp?) is also a problem since these exfoliate fine
particles that float around, could deposit on sections. silica gel stays intact
and is reused for a long time.

Store sections fixed, air dried, in -80C freezer, then bring them
to room temperature BEFORE opening the lid, 20 - 30 minutes.

also stored slides in plastic slide mailers with snap lids, wrapped
in foil, either in a plastic zip lock, or two mailers per black slide
box with silica gel, you can remove one box and keep other for another
day.

These are frozen sections, have stored unfixed frozens in slide mailers with
success, but only for a few weeks.  Fixed sections store for longer times

Label with date faithfully!

Hope this helps.

Gayle Callis