It sounded like fun, so I made this today. I swear I only looked at Nifflas' restricted set once or twice, and I definitely did not copy and paste anything. I hereby release this tileset for public Knytt Stories use, modification, and borrowing. So, don't be upset if someone else uses it first.
Notes: There is a radar screen designed to work with Bank 8 Object 13 by the boat. The boat can be larger by repeating the center tile. The back ground pieces are semi-transparent, not to be used with patterned gradients. I designed it so that tiles in the upper left are on layer 3, the broken girders also go on layer 3. I included interior tiles in 4 colors. You can see how the transitions are meant to work at the right of the sample picture.
If you don't like it that's fine. I admire the look of An Underwater Adventure, and I wanted to see if I could imitate it without copying it.