I use vermiculite as I can buy it fairly cheaply in bulk and I use a lot for to help with drainage in bonsai pots and other containers, but any other inorganic material would do just as well. Your outdoor temps seem fine, I should have said too keep cuttings just moist as they can rot if they are too wet, it's a fine balancing act in that you need to keep the thing alive until it can grow its own root system, without drying out (hence the humidity cover) and with just enough leaf area to keep it going, but not too much as it can't support too many leaves without roots. As I said above, get as many cuttings as you can as it appears to be not an easy species to propagate.

Dave