Can I use Forno Bravo Refractory Mortar to seal Steel Oven Front

[SteveLeBard]

I'm working on my oven enclosure which is metal studs with cement board attached, a 1/8" steel front, and a 14 gauge galvanized sheet metal roof painted flat black. I plan on using the roof for a small solar water heater - hot water for the outside kitchen. The cement backer board will be coated with Quikwall by Quikrete - a waterproof cement product that can be colored. I had the 1/8" plate steel "Oven Front" cut out with a waterjet cutter. There is a small gap (see photo) between the oven arch and the steel plate. Can I use refractory mortar to fill in this space? Is there a better product for this?
Thanks

[Gulf]

I would think that high temp rtv silicone would work better.