another good idea is to put a rag that's soaked in Bleach , in a plastic bag that's left open in the case with your eyepieces , the fumes kill any spores that are in there and stops them multiplying .
This smells a bit when you first open the case but 10 miniutes open in the sun sorts that out .
I do that during the wet season up here and don't have a problem with mould .
Mould is a curse ! .
Brian.