Having used and collected manual Canon and Nikon cameras since 1975 (when I was 11 years old), I have come to some conclusions about long term storage, including the T90 which I love.
My biggest tip is this. Store your kit in aluminum kit storage trunks for sure, or camera bags BUT be careful with the cheap plastic foam that is used for spacing. The type that you cut to make bespoke spaces in a camera storage briefcase, etc. The foam decomposes (even if not visibly) and release breakdown chemicals. This is particularly a problem when the case is closed for a long period of time. The chemical is acidic and corrodes at the microscopic level circuit boards, relays and contacts. I had a EOS 3 that I hardly used that had a corroded circuit bard due to this. And I have had other problems too. I store all my cameras with 'air space' around them in aluminum trunks but with rigid spacers (and packs of silica gel). Gary
