Yes, I'd rather carry my spare rounds in a spare mag. But it's been raining here so much lately I wanted to come up with a WATERPROOF stash box.
If a cartridge doesn't test as waterproof Speer won't sell it under their premium "Gold Dot" brand name. They are sold as generic "hollow points" and the box is marked "Not for L.E. Use -Not to be repackaged - Practice Ammunition". In a similar vein, Remington charges more for their rounds that they advertise as having waterproof primers.
I guess when your life is at stake - like a cop - you worry about things like dropping a mag into a puddle during a firefight.