Archivists recommend standard ambient conditions or a little drier for long term storage. As you've said, too dry and the pages fall apart; permanent damage.

I suppose the fancy silica gels that maintain specific humidities would work in bags.

> I would think this totally dries the pages out and then they just turn to dust, from experience.

They used to sell Boveda two-way humidity control packs that would keep a bag at a constant low-ish 32% humidity, but last I looked those were discontinued (it looks like they've pivoted pretty heavily to marijuana storage and higher-humidity products).