I installed a used insert in a masonry fireplace. The unit came with firebrick, but I'm ignorant of what to do with it. Does the brick just lay in the bottom to protect the floor of the firebox? Also, where do you get the insulation to pack between the surround and stove face? The glass doors I took out appear to have common bat insulation. Doesn't seem very safe with the temps of a wood stove. Thanks.