I have an old Buck Stove insert in my fireplace. Apparently, the fireplace was built around the insert, because it will not slide out. The motor has gone out in the insert and is in the rear of the stove. I need to cut a hole out on the backside of the fireplace. Is there a particular kind of access door I need (cast iron, stainless steel, ect.), or can I just use any type of door?