Usually, it's suggested that you plant three seeds in one
pot and when they germinate, take out the two weaker ones and leave the
strongest one to grow. They're very sensitive to any change whatsoever
and generally, cannot be transplanted.
Water on the tray system but only let it take up enough water
to just moisten the surface and then take away the rest of the water.
This plant, I think, also has a dry season when it wants to be bone
dry.
I don't think you need the propogater cover as this plant grows in
very arid conditions and doesn't need the high humidity you're providing.
Slack's book gives a very good description on how to properly
raise this plant.
Chris