27 CFR §479.39

If more than one business taxable under 26 U.S.C. 5801, is carried on at the same location during a taxable year, the special (occupational) tax imposed on each such business must be paid. This section does not require a qualified manufacturer or importer to qualify as a dealer if such manufacturer or importer also engages in business on his qualified premises as a dealer. However, a qualified manufacturer who engages in business as an importer must also qualify as an importer. Further, a qualified dealer is not entitled to engage in business as a manufacturer or importer.