My personal experience with those types of tins was not very promising. My very first emergency kit was packed in a similar band-aid box. I carried it all throughout boy scouts. When I finally emptied it out after forgetting about it for a few years, most of the stuff inside was ruined. I guess the iodine tablets or moisutre reacted with the metal and it rusted through from the inside out, even though it had some sort of laquer coating inside.
Also, if you wrap it with tape, it's still not very waterproof. And when you actually do need to get something inside, that means unwrapping and most likey wasting your tape, plus you'll probably never be able to reseal it as nicely as it was the first time. It's much easier to find a dedicated waterproof container, rather than trying to waterproof a container that was never designed for it.