masking tape seatbelts

A 2" wide belt in 1/72 scale is going to be only 1/36" wide so masking tape is probably going to be somewhat thick (almost as thick as wide). I'd recommend thin textured foil, such as is found in cigarette packs or on the necks of wine bottles. Either way, cut a strip about 1/32" wide, paint it the proper color, and glue it in place. For wire-style buckles use very thin wire, bend it into the proper shape, and glue it to the "Belt". For solid buckles just use several layers of foil until it is thick enough and then glue it to the belt.