Although special packaging provision PP33 is entered in column 9a of Table A of Chapter 3.2 of the RID for UN No. 1308, packing group II, stating that only combination packagings […] are permitted, packing instruction R001 for light gauge metal packagings is listed in column 8. 

In the opinion of BAM, only composite packaging should be used. At the 51st session of the ECOSOC Sub-Committee of Experts on the Transportation of Dangerous Goods of the United Nations in July 2017, the same opinion was expressed. See point IV. A. (page 9) of the report on the 51st session at

http://www.unece.org/fileadmin/DAM/trans/doc/2016/dgac10c3/ST-SG-AC.10-C.3-102e.pdf