I think a miniature orchid would be your best bet. A phal parishii LOVES humidity(at least mine does) and they are usually mounted on tree fern and such,and smell nice.Also a brassavola perrinii does well and produces really pretty AND nightly fragrant blooms. Do you have any kind of air circulation in the tank? thats a big part in growing orchids......
These are just my own opinion and experiences. these plants work for me but they DO require some kind of air flow. i keep mine shaded outside.
Hope this helps
P