I've heard that they should never be left to totally drain/dry out...they should be 'constantly damp' and your humidity might just be the key :)
Exposure should be full shade, never full sun or else they'll burn
Apparently vanilla orchids only open for one day and wither the next day if they aren't fertilized, not like phals or dens.
Orchids are either epiphytic or terestial. Epi=on|Phytic (phyllum)=leaf. Terrestial=
growing in the ground (these can take more water and some live in bogs. Vanilla orchids are 'epiphytic' orchids and will grow on something but not take nutrients from it (not a parasitic plant).
they cannot store much water because they don't have pseudobulbs (at least not that I remember) hence they need to be constantly damp. They will send out ariel roots to absorb water.