Hi B.
Not sure what batting in the layers you think you should omit...I would use cotton batting though instead of the regular. I use regular batting to lay polymer clay pieces on to cushion them when I bake them in the oven..but my temperatures do not exceed 275 degrees. It's possible the regular batting may not hold up to the higher temperatures of a hot casserole dish, the cotton type will. If it were me, I'd use the cotton outer fabric, a layer of cotton batting, the heat resistant fabric, another layer of batting, then your lining fabric. I think the two layers of batting, and quilted to the other pieces, would you give you years of service.
Let us know how they turned out! and good luck
Woodsy