Okay, my addled brain is coming up with even more ideas that i'd like to try. I am looking to make the SURFACE ONLY of water. I have seen it at the local natural history museum - in the tidepool area. They create with (plastic?) the surface of the water..bubbles etc, leaving the water itself open and airy, so that the details of the sea life can be seen. Has anyone ever done this? or seen it done? I need to create wave action as well..maybe a resin casting? Does the resin stick to latex or will it release from a latex mold? Can the resin be re-molded after it is cured by heating?

I have seen it done (I think) Are you refering to a 'sheet' of water that is the top layer and no actual water material under it?

There was a Gemini space capsule being attended to that used this technique. I would look into using some type of premade mold that duplicates how you want the surface. Pour your resin or water product (I'd opt for resin because its pretty strong). Then peal/pop the hardened surface off the mold and use it in the diorama held up with some type of natural structure like a coral reef or anchor line.

https://armorama.kitmaker.net//features/164

Yeppers, that's the stuff. Has anyone tried vacuum forming anything? Can it be done at home?