Storing Books in Underground Cavern

I'm a fiction writer and hoping to engage some collective brain power here. While I realize this wouldn't be ideal, but IF a collection of valuable books had been stored in an underground cavern, at a steady 56 degrees but higher levels of humidity, WHAT could be done in the storage to best preserve the books over many decades? If they were stored in a crate insulated by shelled corn or wrapped in linen, would this help? Anything else that could function this way? Thank you!

Corn -- probably not a good idea. In time it could sprout or mold, depending on how dry the cavern was. Corn could also attract rodents that would be all to happy to have found a stash of books too. Humidity and actual damp would be a major problem no matter what your stash of books are stored in. Judging by your choice of packing material, this must be a pre-plastic time. Wrapping in linen is a good idea in sturdy, well-made wood crates. Just wrapping them very tight and packing them fairly tight would be one of the best things you could do, decreasing exposure to air.

Bona fides: I've studied archaeology, am a professional historian, and museum curator, though these days I deal mostly in very recent history: https://www.washingtonpost.com/arts-entertainment/2019/08/15/how-woodstock-bird-...

The books are almost certain to get moldy after not very long, unfortunately. It's just a fact of life with books that if they go over 60% rH they get moldy eventually; the higher the rH the sooner it happens, and it looks like cave rH is basically 100%.