I've got a similar setup- my pan is stamped steel, kinda corroded when I got it. I cut a section out of a plastic plant pot ~ 1" high to form a collar, slightly larger than the grate and laid in some refractory cement I found at my local (non-big box )supplier. Made it an inch thick, and I can replace the grate as necessary. Needless to say, once the cement cured, I pulled out the plastic. After a few fires, a crack developed, but that's inevitable. and my pan oughta last a while longer.
Steve