Following on from my first post, drying out of optics should not be relied upon by desiccants!
Desiccants actually have very small moisture capture capacity. These should not be used as an active drying system as they will saturate very quickly. If moisture has been left trapped inside desiccants will do very little to nothing at all. Desiccants should only be used as a stop-gap measure only after an item has been thoroughly dried to begin with.
Additional to this is ventilation & storage conditions. Sticking an item down the back of a cabinet is a fantastic way to have mould take hold. If there is no way for air to move about then this is the perfect situation for mould to take hold. I have seen countless scopes and other optics be destroyed by mould because they were poorly stored. And a box offers no protection especially if there was moisture trapped inside the item.
My man-cave is a converted garage. It is well insulated but being a garage it isn't a great structure for ventilation or at keeping out the damp. Being in Sydney doesn't help. One day I noticed a musty smell. I pulled back a cabinet and found there was mould growing behind it. VERY BAD NEWS! I first looked at desiccants for my gear and found out in just a couple of days that this stuff is not suited for storage even though the gear appeared "dry". The next step was getting a dehumidifier. I got a unit that also has a hose attachment to drain the water these units collect as a tank fills up quickly and if I don't empty the tank every two days the tank fills and the dehumidifier turns off - it is amazing how much water these units pull out! Just with the first overnight use of this unit and straight away I noticed a difference in the air in the man-cave! I have also noticed that some mild steel items I have in the cave have slowed in their rust development! BIG BONUS too! This little unit is doing a great job. I also use a small fan to help move air around and improve the efficiency of the dehumidifier. When I bring in my astro gear I leave it open without any plugs or caps to dry out at least overnight, covered with a cloth of course. Only once thoroughly dried out do I squirrel away the gear.
I still through in silica gel in with my gear just as an added measure should the dehumidifier break down for a long period. But these colour changing beads now last a lot, lot longer before needing recharging.
Too small a unit and it doesn't have enough grunt if the area is too large, too big a unit and it is a waste of power - another thing to consider when selecting a dehumidifier.