I'd say: go with the wood panel idea, you can get some thin plank or a decent looking piece of ply cut to size for the walls of the hole, sand it lightly and varnish/oil it to make it look a little nicer and polished.

Then surround the edges of the laminate flooring above and the ceiling below with with edging profiles like this:

https://www.brico.be/fr/atelier-materiaux/quincaillerie/profiles-toles/profiles/nez-de-marche-3m-strie-36mmx18mm-170cm/10052393

You can probably find brass, wood or black ones depending on what you think would look nice.

Personally, I'd go with wood edging strips stained/varnished to match the siding wood and the upstairs flooring, but it's not my home - you do you and make it your own.

The lack of a protective atmosphere would probably leave it far more exposed to radiation if kept on the surface or in a container that isn't lead-lined or the like, which would probably degrade the paper...

But this is getting more convoluted and more than my limited knowledge and understanding can provide for - your best bet might be to reach out to Randall Monroe of XKCD.

Heck, it's the kind of question that belongs in his book: "What If?" https://www.amazon.com/What-Scientific-Hypothetical-Questions-International/dp/0544456866

It depends on the chemistry used in the process, amongst other things, but probably not.

Regarding the chemistry - older (and some sulphur based modern) methods of bleaching left mildly acidic residues in the page and these caused the paper to brown over time, accelerated slightly if the paper had been exposed to the fatty acids in sebum from people's skin.

Newer methods supplement bleaching with a filler material such as calcium carbonate, partly to reduce the wood pulp required, partly to reduce the amount of treatment required to achieve a white product at the end of the day.

Pages produced in this way have little, if any acid residues and should remain white for a much longer period of time, I doubt if it would do so indefinitely though - oxygen in the air, microbes on the surface or other factors could result in slow degradation and discolouration over time.

No, I could be an asshole too...

When he was complaining about all of us working in the garden, saying "I'm Booooored!", I handed him a pile of vines and asked him put them in the compost.

A few minutes later, a cry of "aargh!" as he lifted the lid and fled with the fruit-flies formed a micro locust swarm around him.

My excessively chipper "Well, at least you're no longer bored!" was met with a shivver and "Byeurk!" of disgust.

Been there and I know. I'd usually aim to steer it towards becoming a loop and then point out that I'd answered that question and start getting mock worried that if his memory was that poor, he clearly wasn't getting enough sleep!

Fair enough, I always answered until it reached a loop and then I'd point out that I'd answered that already. Then start ignoring any repeats or suggest that if their memory was that bad, they clearly needed longer naps or less sugar. That usually worked without appearing to give them the win of me losing my temper or speaking down to them.

I have to disagree with this, I like to see it as an opportunity for learning.

I ended up taking my little brother through the water cycle as a toddler using analogues he could relate to - such as steam from a kettle or pot as well as condensation on a cold window.

We got through it by the time we arrived at his preschool and he never asked why it rained again and all through his childhood, he knew that I'd talk to him seriously and answer his questions.

He's now a fan of theoretical physics, and studying towards that end at uni.

Nurture their curiosity, no matter how weird or trollish it may seem.

Just putting this out there, but if he's 62, and from the sounds of it, hasn't had a long term partner that the family has mentioned before...

He might not be into tits either, yours or anyone else's.