How about structo-lite in place of the perlite concrete mix? It does say not to be used in an area that could get wet. So that being said could it be used as it resists heat and is less than half the weight as sanded plaster? About 12 dollars a 50# bag?
Welcome to the BrickWood forums, Johnny!
It’s an interesting idea, since Structo-Lite uses Perlite as its insulator.
After reading the data sheet, I’d say it’s problematic. As you mention, it’s not to be used in an area that could get wet. In ordinary conditions the insulated slab is protected from water, but it’s quite possible for accidents to happen (like leaving the door off during a blowing rainstorm).
The material itself demands much stricter attention to ambient conditions when it is being applied, especially the requirement of 55°F air and surface temperatures. Since it is being laid into a concrete slab that acts as a big heat sink, you’re unlikely to get that.
The simple Perlite/Portland cement mix doesn’t need that kind of attention, and you can even pour it into a damp slab. The difference is that Portland cement generates heat as it cures (plaster does that too, but to a lesser degree).
One more thing: the P&P mix (I just coined that!) will cure into a rock-hard surface that can bear the load of sand, brick, wood, and food. If you were to spill liquid into your oven, you might crack a firebrick but it will have no effect on any of the surfaces below including the insulation layer.
I’d recommend staying away from the Structo-Lite as a needlessly complicated and marginally unsuitable material. The P&P mix is easy and cheap, as is its cousin Vermiculite/Portland cement. The latter takes a few days to cure as opposed to 48 hours for the Perlite, but they are both incredibly inexpensive and do the job.
Thank you again I have used the structo-lite on door jams for fire protection before then I seen the data sheet as well but didn’t think about getting a nice juicy steak that juices could spill. I will enjoy building this for real, as the past couple of days been setting it up in my dreams, sleep, Actually no sleep this long weekend I will start. Thank you again
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That’s how this project gets you! 
Seriously, you build it a hundred times in your mind before you start excavating for the base.
If you can, take lots of pictures of your process. I know @BrickWood really enjoys having them on the site so others can be inspired by what you’ve been dreaming about.