I have two plants of Miltonia spectabilis. One is on cork with a small pad of spaghnum and the other on a tree fern plaque. During warm weather they get sprayed daily or dunked in rain water and during cold weather they get watered about twice per week. The roots are extremely fine but don't seem to mind drying out. My plants are doing quite well. I don't know how to advise you about keeping them moist but I can tell you that they certainly don't have a problem with drying.
I have about 36 mounted Aerangis/Angraecum orchids. I water them all every day - some get dunked and soaked for 20-minutes. The leaves will show you if they require water - many of mine will shrivel and wrinkle and become quite limp if they are not kept moist. They all tend to dry very quickly. I'm sure as the weather gets warmer as Spring approaches than into Summer, I will have to water them more than once a day.