Reddit mentions of Kirkland Moisture Absorption, Clear

Pack them away in storage containers (the kind you get at Homac or other DIY stores, and include dessicant -- if you are not afraid of them being tipped over (ie: earthquake-proof them), then you could put in the big humidity sucker thing. It's made for closets, but I think you'd feel more safe by putting them in a semi-sealed thing like these storage containers.

Here's a link to the humidity suckers: the brand I know is mizu-tori zou-san. https://www.amazon.co.jp/%E6%B0%B4%E3%81%A8%E3%82%8A%E3%81%9E%E3%81%86%E3%81%95%E3%82%93-%E3%82%AA%E3%82%AB%E3%83%A2%E3%83%88-550mlx12%E5%80%8B%E3%82%BB%E3%83%83%E3%83%88%EF%BC%883%E5%80%8B%E3%83%91%E3%83%83%E3%82%AFx4%EF%BC%89/dp/B0093W80QW

For your very important papers, you might consider a large tupperware container that actually seals.

Be sure you clean the apartment and try to get it mold-free before you leave. If there's nothing to grow, there won't be so much from "immigrant mold colonies".