The propagator used 4 watering trays lined with metal film bubble insulation.
A heating cable was laid on top of the bubble insulation to reflect the heat onto the underside of the seed trays.
Each of the trays was left on the propagator for one week to allow the thinned out transplanted seedlings to establish themselves before the trays were transferred to the heated sand bed in the greenhouse. The temporary propagator set up has been very successful given how quickly it was set up and how relatively primitive it was.