The link below gives instructions on how to make a model of a container, an provides a downloadable pdf as template.
Although it's ostensible to be used as a tissue box, if correctly scaled and if the slot for tissues is ignored it could be useful to produce containers in card or plasticard.
http://www.instructables.com/id/Shipping-Container-Tissue-Box/?utm_source=newsletter&utm_medium=email The template is on page 2 of the guide.
The site - Instructables - gives loads of useful (and less useful) guides to all sorts of stuff which could be handy for wargaming too. You might have to register, but the 'lightest' registration gives you a daily email (almost) with links to a selection of stuff (you can choose the themes to your liking) and no other obligation - and no fees.