This has to be more simple than our minds are conjuring up!! We are planning to install a vent insert over our stove. The piping is in place, we will purchase a 36" insert, and blower. What is the typical way to install one of these when no cabinet is being used?? It will have a rock surround like in the attached photo. Our entire opening will be 6', so what do people typically do to cover the openings on each side? I can't find photos looking up into one of these spaces other than when cabinets are used.

Please give me some insight!