[Koha] Items in offsite storage

If any libraries have documents in offsite storage I'd like to know how you use Koha to indicate their location at the storage facility, i.e. box number etc., to identify items for retrieval if and when required. I'm particularly interested in how to deal with individual issues of serials. The company I've been talking to add their own barcodes which could mean having two barcodes per item, ours and theirs. Description: OpusDianna M Roberts Manager Information Centre Opus International Consultants Ltd Dianna.Roberts@opus.co.nz Tel +64 4 471 7250, Fax +64 4 473 1075 <http://www.opus.co.nz> http://www.opus.co.nz Level 6, Majestic Centre, 100 Willis Street, PO Box 12004, Wellington