If you are looking for the best storage boxes, these, made with Microchamber board, are it:
http://www.conservationresources.com/Main/section_5/section5_19.htm
You can read the technical details here on Microchamber:
http://www.conservationresources.com/Main/S CATALOG/TechnicalInfo.htm
Most top museums in the USA use this. I also understand that Disney's Animation Research Library uses it to protect their old animation cels.
The company is quite old-fashioned in that orders are taken over the phone only, but they are very helpful and accommodating. I have had them do custom sized boxes for European size 12X16 prints, but most of their standard size products ship quickly.
The products are reasonably priced, but as always shipping is the killer. VPOST USA is the cheapest option, but always buy in bulk, as they offer volume discounts.