Orchid Terrarium (especially flooring) suggestions?

[Stripeyiscool]

I recently got a couple terrariums for free off Craigslist. The first one I want to set up is what I think is around a 55 gal tank. it is one of the lengthy ones. I have a plan of putting is branches which I could mount bromeliads and mini orchids on. I have seen people put gravel, dirt, a mix of those, moss, etc. I sort of like the moss or the dirt ones except Im not exactly sure if I should be able to plant plants directly into the dirt or media that would be flooring. But then it would get to moist? Im really kind of lost with this. Anyone done this before and can give some suggestions or maybe even some pics? (Also posting this on the orchid forums)

Thanks!