Here is my long overdue modification of your previous sea containers.
Basically they are compressed into fitting tiles allowing you to create the sea containers to be any size you will, with the addition of a shadow rile that you can use to have above player to simulate the height, the top side of the sea containers can also be set to above player to overlap and display it's height.
Sadly i'm having serious trouble trying to use this tile sheet in the rpg maker, I think some of the positioning is a bit off.