What license is it under?
Copyrights here only affect the actual drawings of the product. By default, the author is granted copyrights. That means you can't publish your own book with those drawings, for example.
But to actually build the chassis, go for it.
It's not under any license, it's just 'free'. We've talked about putting the Storage Pods under a license, and may at some point since we get this question periodically and picking a license that people are familiar with may make it more clear that we really are giving away the design.
If you start selling them as your own product, maybe that would be an issue.
The creative commons and OSI are two excellent places to start looking at licenses. creativecommons.org and opensource.org
To be clear on our philosophy - we don't want to restrict people from building these for their own purposes, modifying them, giving away the design, selling the boxes, etc.