I am new to the board and have been looking at vivarium builds for the last two days. I have many questions that I am hoping someone can answer....and sorry if they sound stupid =]

I have a 18x18x24 terrarium (Exo Terra - Natural Terrarium with Sri Lanka Background - Small/Tall) that will house 2 Whites Tree Frogs and 1 Blue Dumpy Tree Frog. What my husband and I are hoping to achieve is a vivarium with part land and part water. We will either construct the land portion out of egg create, GS foam and silicone or out of clay. Can anyone give me pros/cons for either? Also, we are hoping to create the land portion to be water resistant so that no water can seep behind or below the land. Is the only way to do this by siliconing the land to the terrarium?

Any next series of questions would be bedding and cleanliness. By creating the land portion I am assuming that I will not be removing the land and thouroughly cleaning the vivarium but rather spot cleaning, correct? And with creating the land out of either GS foam/silicone or clay how would I incorporate the bedding on the land? Would I just silicone the bedding onto the land or is there another way this can be done? And how can it be cleaned? (Cleanliness, as well as waterproofing, is my huge issue) We will be incorporating plants into the vivarium.....and in the water section we will have filters to keep that area clean.

I guess my main issue is which construction of land is better, how to keep it clean, and if it is possible to create the land and incorporate it into the vivarium without water seeping behind or underneath. Thank you for any advice or information!