my underwater world was water to start I'm slowly building it all in, I use dirt to fill the glass areas and take the water out Daz helps me with that side of things feel free to come visit if you haven't already
I have a few underwater domes on frontier. I used the fence post method with jackolanterns for light. Started in one corner set 2 posts on top of each other. Lay out some of the base wall with a small entrance. Go around the building laying a couple fence posts again every so often. 4-6 is what I usually use. Once have a nice frame/dome/etc, enter where we left a doorway. Fill the inside with sand over dirt. Use torches to speed remove the sand. It can still be pretty slow to remove the water inside sometimes, but seems a good method. On frontier I have 3 underwater domes in the ocean for animals, my cattle dome works pretty well for me
