In the last weeks some researchers did some research in behalf of the Toy Museum in Nuremberg how to store old Barbie dolls the best way. The researchers found out that it is the best to store the old dolls in a cool, dry and dark environment. Here’s the link to the German article http://www.deutschlandradiokultur.de/spielzeugmuseum-in-nuernberg-barbie-forever-young.1008.de.html?dram:article_id=379793 .
I don’t know if this was published in English speaking countries too. If it’s not you can use google translator for reading it.