I used regular (not black) Rutlands Furnace Cement.. Similar to the one shown in the link below:
It does not need curing at 1200 degrees but can withstand temps of up to 1200.. You might double-check what you've got -- it is probably fine and does not cure at 1200 but can take up to 1200.. Start out with the low-n-slow temp cure as indicated elsewhere.
Make sure you use a thick layer to ensure no cracking.. I'll have mine on the inside and outside to make a nice sandwich.. You can also thin out the Rutlands to make it easier for the application.. I thinnned mine out to be perhaps a bit thicker than yogurt.. YMMV!