I had a similar post with that question a short while back. I think the most cost effective soloution for me to avoid the temp changes and salt ait in Cape May NJ is to build a small closet in my garage and install a small combo air/heat unit to keep it above freezing and below boiling and also keep the humidity down
A tech answered me and said the worst is leaving your keyboards and such in a closed car. That I have tried to avoid all along
Good luck
Bill in NJ
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer