As soon as they have popped the surface they need both humidity and fresh air, so don't over-do the propagator. I always manage an almost 100% success rate without using a propagator by just popping some zip bags loosely over the top of the pot. It keeps in some humidity, but also lets air in, and seems to work almost every time.
Temps should be between 20-27C, slightly warmer during the day than the night. Soil temps shouldn't drop below about 16C.