It's really easy to put an internal hard drive in an external casing.
[Image: https://i4.minus.com/iblzOowAz4zogg.jpg]
This is a hard drive. It might be thinner or thicker than this. It's decently sized, but you can hold it with one hand. It's a raw, unprotected computer part so it does look a little unusual.
[Image: https://i3.minus.com/ibtoK2sEFEUGfy.jpg]
This is a dock. You literally just slide it in and it works.
[Image: https://i.minus.com/i2r9zL63OroFs.png]
And that's a slightly more secure hard drive enclosure where you still just slide it in. In this picture, there's a hard drive in it that's sticking out partially to show how it fits right in. Anyway, you push it in, tighten a couple screws, and it's in there securely and will function as good as an external hard drive.
If you can charge an iPod, you can use a hard drive enclosure.
Just make sure they're compatible.