I switched to Cyprus mulch and had a good time with humidity with it. In a glass tank, with a room humidity of 30%ish, I was able to maintain 50-60% in the tank by misting twice daily. I've since switched to Exo Terra Jungle Carpet (as the store was out of mulch) and I personally like it even more.

I baked it at 350 for 1 hour prior to use (and letting it cool!) and it still retained moisture. When I misted it, it sucked up any moisture that was lost.

I cover about 25% of the screen top of the viv with aluminium foil (shiny side down, and leaves lots of room for air flow), and a small towel on top of that. It traps heat and humidity quite well. I also use a ceramic heat emitter in place of a light, as it does not affect humidity, and it maintains ambient air temps of 80F.

Hope that helps!