Hi Neville,
I have two dewshield wraps for the 9" Mak. The shorter one has foam rubber, yes, but on the longer one I have used black felt contact. The foam rubber I find too thick and not black enough.
Don't use any heat! This is the entire purpose of this method of dew control - it is thermally passive. The insulation slows down to cooling process, enough for a heat plume not to develop inside the OTA. Introduce a heat source to the rear of the OTA and you will re-establish a heat plume inside the OTA as the inside of the scope will have cooled down.
One layer of the Coreflute is plenty. The Velcro does keep the Coreflute tightly wrapped around the OTA. Coreflute is just one material that can be used. You can use whatever material that is at hand. The only thing that you need to do without exception is not have the OTA section of the wrap black in colour. Black will cool below ambient temperature, and will work against the very things you are trying to achieve. The pic below shows how I have laid out the black felt inside the wrap, but free from section that goes over the OTA.
Have a read of this following link which talks about the insulation of Maks and SCT's:
Maksutov and SCT insulative dewshield
Alex.