> How do you know when the desiccant is saturated?
Buy dessicant that changes color. I bought some from "Dry & Dry" on Amazon. When the color change indicates it's absorbed a lot of moisture, dry it out in the oven or microwave.
> Ziploc bags
I store my spools in Ziploc bags, from which I've sucked out most of the air through a straw. I see that the Ziplocs eventually reinflate back to atmospheric pressure (no longer sucked in tight to the filament). So Ziploc brand is not perfectly airtight. I'd like to see suggestions of better brands or sources.