So yes, this is another techy, geeky post. But maybe it will help somebody… Or even remind me later how I solved this when I come across the problem again.
What seemed to be happening was after a certain amount of inactivity, when left on this new hard drive enclosure (presumably) does something that makes the OS say ‘hey, you’re inactive… I will put your drives to sleep’ and then proceeds to disconnect everything very abruptly.
When I dug a little deeper I learned that there is an Energy Saver setting in OS X that controls whether the hard drives sleep or not. It seems (at least for right now) I need them to not sleep. (I imagine this includes external and the internal drive… So I might want to research this a bit more with respect to the internal drive.)
All I needed to do (it seems) is uncheck the “Put hard disks to sleep when possible” option, as seen in the screenshot.
Another thing I learned about while prepping for this post was some nifty features about the “Preview” app in OS X. I’ll have to save those for a future post. But in the meantime, you Mac users, you really should check out the hidden power of Preview!