Required parking spaces may not be rented as, or used for, vehicular storage. However, additional external storage area may be provided for the storage of privately owned travel trailers and/or boats, so long as such external storage area is screened from adjoining residentially zoned land, parcels on which a residence exists and adjoining local roads, and is located behind the minimum yard setback lines. This provision shall not be interpreted to permit the storage of partially dismantled, wrecked or inoperative vehicles.