Starting a terrarium

G'day all, i've been wanting to start up a terrarium for a while now, i had a crack but it failed miserably so hopefully someone here can help me out. I want a fairly basic rainforest floor terrarium for trapdoor and funnelweb spiders. Main thing i'm stuck with is the substrate and getting it so it wont be water logged so plants will survive. Its a 3ftx2ftx2ft tank so there is a bit of space to fill. Basic idea is the rainforest floor with some rocks, bit of wood and some mosses, ferns and any other small rainforest terrestrial leading up to a small vertical bank covered with mosses and ferns as thats where alot of trapdoors like to burrow. The typical substrate that naturally occurs on is a clay type substrate but thats heavy so i would prefer to just have the top 5-10cm as that just for looks. Not sure if this will work but i've been thinking about it for ages and its bout time i get on with it. Any tips or ideas would be much appreciated,

Hornet