Can Masdevallia tolerate low humidity for extended periods of time?

[Roberta]

I agree, depends on which ones. Some are more tolerant of both low humidity and higher-than-ideal temperatures, than others. You can "extend the range" a bit by using two nested terracotta pots, and sphagnum. So you maintain some extra humidity around roots, and also get evaporative cooling. You just have to try... you won't have 100% success but the survivors are very rewarding.