Over time, yes. However, they float for some time when washed overboard during ocean transits are are actually a navigation hazard in major shipping lanes until they sink. A 100 year flood would prolly get them wet. An az monsoon not so much. I'd wager in a hurricane yo'ud have good odds of keeping stuff dry depending on the storm surge and lingering flood water if they're sealed.I am positive that water would definitely seep in.
until they rust through.