The people who installed a gas insert into my prefab fireplace didn't take into account the fact that the firebox sits about 5.5 inches above the hearth So the air intake of the old firebox is exposed. I need to fabricate a slab of metal about 5.5 inches wide and about 36 inches long and about 3.5 inches thick that is tappered at the edges. It should match the black cast iron surround. Assuming cast iron would be too expensive to fabricate, could sheet metal be painted with a rough texture so that it looks like cast iron? (The sheet metal could be a hollow boxy shape to provide the right thickness.) How much would something like this cost? Where could I get it made?