Least dangerous. I recommend storing them in a shed next to your home. Thanks for stepping up. We appreciate you.
Happily. As long as I also receive a billion dollar check and the necessary permits for digging a ridiculously deep shaft straight down.
The issues surrounding long term storage are almost entirely political.
You are acting like this is some kind of gotcha...I literally would do this for extremely reasonable sums. Unless you are grinding up and swallowing these materials (which requires that you first break into their storage casks), they are not at all dangerous.