Whenever possible, drill a diagonal hole into the stem, and fill with Roundup concentrate from a syringe. Buh-bye.
If you have a hypodermic, you can inject it into non-woody stems, too. Very, very effective on large kudzu.
There was a bunch of mold and rust under mine that I left on the concrete basement floor for years. I don't think the safe was really damaged, but only a matter of time. A moisture barrier is good.
BTW, for anyone that doesn't know... TSP is the phosphate that's now illegal in dishwashing-machine detergent, and laundry detergent. If you add a bit, it will clean like in the old days, when you need it. Dishes or clothes.
Be sure to confirm legality first, of course.
...and replace them with Apple. There's no way to get away from them if you have an Android phone. There may be some viable alternatives though some day soon.