Help with Terrarium set up for masdies

[Werdna]

everybody I'm new to the forum
I live in tucson az and I have always wanted to grow masdevallias, but considered them impossible to grow in the desert. Looking through the forums the last few days has got me thinking, , what if I set up a small terrarium for them in my room? I have very limited space, I could probably fit a 10 or 20 gallon tank for a few of the smaller varieties. The temps inside my house are usually in the 70s with about 6 degrees of difference between night and day, however as summer progresses this difference will shrink. So I guess my biggest question is How do i keep the temps at an acceptable level for the masdies and how do I give them a big enough temp drop at night? Also how do I keep the humidity high enough while keeping adequate ventilation in such a small tank.
Thanks for any advice anyone has

-Andrew