With the factory legs the stove only needs ember protection, but that is based on testing the stove under full load. Because the stove is off-label with short legs, the hearth's insulation requirement will be a guess. In the least, I'd put a sheet of metal, then some micore before the top layer of 1/2" cement board. The stove is 31" long and the hearth should extend at least 16" beyond the front door of the stove, so this will be a very deep hearth for the 118.
