I think the easiest and most common thing I've seen people do is to affix egg crate to the sides of a tank, and just hang the mounts on there. Here's an example I found from a quick googling:
This is pretty handy because most "mini" orchids you'll buy will come mounted with a hook; this way you can easily hang them on the egg crate.
OH and a some people will drill the tops to add misting nozzles for automatic watering.
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