i think you have it right with the semi-moist eco-earth.
if i was going to do anything, i'd add a tiny amount of cypress and sand to give it the natural look. i really like the way cypress and eco look together.
are you gonna do live plants? you could have pothos etc. if you are really gonna go natural. i love the way kings navigate a thick bed of pothos. it's not a completely accurate naturalistic plant, but it serves the purpose, grows super fast and is an introduced plant almost everywhere.
i dunno, give up the pics whatever you do! good luck