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is it OK to leave it outside on shelf with few silica bags around it?
Silica bags will do nothing if they're put on a shelf, they need to be in an enclosure to have any effect.
The other thing to watch out for is that silica gel saturates, after which it stops being effective. It can be renewed, but you have to know when to renew it. I would suggest getting the following:
1. A pack of indicator gel (lots available on Amazon). Indicator silica gel changes colour when saturated; you then throw it in an oven at 250-300 degrees F for a couple hours hours to renew it (indefinitely).
2. A reliable humidity meter to throw inside the box, so you can verify that things are working. Just buy a digital one with good reviews.
3. A translucent plastic box with lid to put everything in. (Light also deters fungus.)
You can get all of this for <$30.
If you're willing to spend a little more, you can get a powered dehumidifier cabinet.
Whatever you do, do NOT store lenses in your camera bag indefinitely. Bags harbor humidity and germs and are a great fungus growth environment inside. Whenever you get home take your lenses out and either (a) put them in a box as described above or (b) take off the caps and leave it in a bright area for a few hours while before storing -- fungus hates sunlight (but make sure you don't leave the rear cap on and put the lens in the direct sun, which will melt a hole in your rear cap and smoke up your rear element)