Tried some different variants of the two thumbnails I liked best.
I really liked the ones where it sort of jumps out of a wave, or is about to do so. It really gives me that "it's over" kind of feeling, where all hope is lost.
Same goes for the one where they're swarming beneath a ship. Having them circle around it more, really help sell the underwater look. That said, I think that would require way more effort to get something with less impact than the one the jumps out of the wave.
So i'll be going with one of the two images depicting it inside a wave from the first image or a mix of them. Something along those lines...