I think the best way to do a plaudarium is to use a course substrate to build the general shape and slope of the land areas, and then cover with sand or crushed coral. I have been planning out a mudskipper tank. I have given up on making one with live Mangroves, because of how high they grow. I hope to have about 6-7" of water with a 1" substrate building to 7-8" tall. That will give me about 5" clearance to put in some "vines" and "branches" for the crickets to crawl on and be shot off by the archer fish. This will have several "islands" and that means several muddies. I don't want too many crabs, maybe 2 or 3. This will be in a 40 gal. breeder. I hope to be able to get 3 archers and 5 muddies in there. I will use some broken lava rock to make the general form of the "islands," and use a mix of crushed coral and play sand as the substrate. This will hopefully prevent anaerobic spots, and raise the pH and gH. Eventually, I want to buy a mist machine, and that will allow me to put a screen lid on it and retain some humidity. Then, I can increase the level of the land to almost the top of the tank, and build a "cage" lid that maybe is another foot tall. Then, I can have live mangroves. But, that will have to wait.