I'm probably opening a can of worms and hope this hasn't been discussed elsewhere. Has anyone tried using casting refractory cement over a dome of foam. I was thinking that with the base, hearth and cooking surface in place one could place a foam dome shape, probably covered with some sort of plastic sheath and an appropriate front opening accounted for, on top and just trowel over it. Cut out the foam and build a vent. I'm not a mason by any means, so pardon my simplistic approach.