[dmun]

It's hard to make generalizations about insulating castable refractory, because there are so many different products by various vendors for multiple applications. If your enclosure is pretty tight, there is nothing wrong with loose fill vermiculite, the only thing is that it tends to leak out of surprisingly small joints. The blanket is more efficient, but also more expensive

I do know that the outside of your insulated dome should be lower than 150 degrees. Mine's behind a masonry wall, but it hardly gets warm to the touch.