I'm unsure if this is the correct community, so feel free to move it if you feel it's in the wrong area.
I'm trying to develop a water-tight/sealed box for a backup flash drive. The idea is to make something that is weatherproof enough so I can keep the box outside or in my basement for years, and if I ever need to retrieve the data, I can cut the box open and retrieve the USB stick. This would need to completely resist water/moisture and withstand temperature changes between say -40 C to 40 C without it breaking down.
Here is the concept I have so far:
First layer: Put USB stick into air-tight plastic container. Could be something cheap like a sealable zip-lock bag to protect from:
Second layer: fill a small box - not much larger than the stick - with a polymer sealant/caulk that will eventually solidify, fitting the form of the box.
My question is, what is the best material can I use for layer #2?