Here in inland Southern California we have pretty low humidity as well. Generally, I've found that increased watering for mounted orchids can compensate for low humidity. Increased watering means less medium but that's what epiphytic orchids prefer...again, generally speaking.
For example, I have a
drip system run up my Cedar tree. When night time temps are over 55F I run it at night for around 20 to 30 minutes every other day and by the next morning the roots are still damp. The orchids then pretty much dry out during the day.
But in my shade shelter area I have a few mounted Pleurothallids and Bulbophyllums that stay pretty evenly moist. Dendrobium is a huge family so it's hard to identify the watering requirements without knowing the group it's in. Sherry Baby can definitely handle drying out between waterings but might be able to handle staying evenly moist if it is actively growing and mounted without any media. The Phalaenopsis probably has the highest moisture requirements and can probably best handle being evenly moist.
There are 1000s of species of orchids to choose from and probably quite a few that are perfectly suited for the conditions that you can provide them. What might be fun to do is to research the epiphytic orchids that come from the same place as your chameleon.
In terms of water quality I'd say that 60 parts per million is really good for orchids.