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Helinox says:
Versatile, and incredibly useful, Helinox Storage Boxes securely fasten to Helinox chairs and tables for secure, instantly accessible storage. There’s no end to what you can use them for. Stash little things like keys, phone, and wallet. Size up for a box to store food and drinks or a windshell, book, and water bottle. Go up to a medium to handle your campsite’s kitchen gear or a puffy or two.
Made from durable polyester, they have padded sides to protect the contents and hold the structure. MOLLE-style attachments with a snap closure keep a secure hold on your Helinox chair or table, and external lash points let you clip on extra gear. Three sizes give you options. Extra small is 4.5 x 4.5 x 5.5 inches [11 x 11 x 14cm], small measures 14 x 4.5 x 5.5 inches [35 x 11 x 14cm] , and medium comes in at 18 x 6.5 x 7inches [46 x 17 x 19cm].
We're working out what we think about Helinox's Storage Box XS, we'll add our comments here in due course.