https://www.amazon.com/Vittles-Vault-Outback-Airtight-Container/dp/B0002DJOOI
lolol if you needed a link or don’t know of an airtight container just ask. continue storing your stuff in there and let water get in it as you please. Whatever makes you happy at the end of the day my friend. It’s also factual that gamma seals are air tight but your observation is anecdotal.
I believe Mailvelope is the software I usually recommend for Windows users. You'll probably have no trouble getting it working. We could also go over something not browser-based like Kleopatra.
On Linux, GnuPG is the goto software. On a Debian based distro all you need to do to get it is type apt-get install gpg. That is, if it isn't already installed.
Congrats on the new property! I hope it becomes everything you want it to be. It sounds like you have some good basic goals to achieve and with some good planning, should be fairly easy to achieve.
The rain barrels are a great idea. Be sure to think about an electric pump. My barrels are fairly close to the ground, so I don't have enough head pressure to water directly from the barrels without a pump. My garden is fairly small, so I don't mind using a watering can.
I think renting your roof out to produce solar, only to still lose power when the grid goes down is a poor trade off. I got a quote a few years ago for a 5.3 KW system that was only $17,000. With financing options and a down payment, you can own the panels and keep your electricity on when the grid goes down.
I also recommend the book "The Backyard Homestead" and the companion book "TBH Guide to Farm Animals."
Good luck on your new adventure!