Air conditioning units also function as dehumidifiers.
That's why merong tulo pa-palabas ang mga aircon: that is all the moisture that's been removed (via condensation)
from the air in your room.
Air conditioning aside...
If you have a decent hardcase, a few sachets of dessicant will do for as long as the hardcase is sealed. Upon first
exposure to rainy-season humidity will rapidly saturate the dessicant, and then it can become a focus for mold
(kasi many dessicants are partly-organic --some are even starchy)
... so if you're putting a guitar away for storage na matagalan in a good hardcase, okay ang dessicant sachets, but
if you are going to be opening and closing the case weekly or more often, useless ang dessicant.