After designing and building our custom electronics for the Tympan, it was clear that we needed an enclosure to hold it all together.  Using zip ties (my usual go-to solution) just wasn't good enough.  I needed something more proper to wrap around and protect the electronics.  I was kinda nervous about taking this step because, if you've never designed an enclosure before, it is HARD!  Here's a quick picture tour of how I got to a workable enclosure.  Yay pictures!
Making Something Attractive?  Normally, one wants an enclosure to be both functional and attractive.  As I started into this task, though, I very quickly learned that "attractive" is not really part of my skill set.  It's especially challenging  when the electronics (ie, the bulky guts that I'm trying to cover up with my enclosure) have already been designed and built and can't be altered.  This imposes some challenging constraints on the enclosure.  So, I set aside the goal of making it attractive and I focused on simply making it functional.

First Attempt:  Working with a fellow engineer who knows more about CAD than I do, we decided to use a two piece design that would sandwich the electronics and battery.  We'd 3D print the two pieces of the enclosure and hold the whole thing together with four small screws.  As you can see below, our first design ended up being pretty boxy.

Our first design.  Boxy!
Begin the Revisions!  Seeing it on the screen, I could begin to visualize in my brain how I might want to hold and use the device.  I decided that, if I was wear this device, I'd most likely keep it in my pants' pocket.  I decided that the boxiness of its nose would make it hard to slide into and out of my pocket.  So, we revised the design to make the bottom cover slimmer and we put big slope on the top cover.

Revising the design to make it slimmer and easier to slide down into a pocket.
Iterate, Iterate, Iterate!  With the overall configuration taking shape, we began to make lots of little changes to accommodate the battery wires, to give better access to the volume pot, and to expose the LEDs (box #3 below).  At this point, I decided that the sloping nose made it harder to get your fingers around the volume pot, so we we removed the slope (box #4).  This is the design that we used for our first 3D print.

Real-World Experience:  With the real, physical print of design #4, we were able to put it all together for the first time -- electronics plus battery plus top and bottom enclosure.  Almost immediately, I realized that I needed access to the Teensy's reset button, which was covered by our enclosure.  Oops!  So, we added a round hole to expose the reset button (see #5 above).  Then, we further expanded the hole to expose the SD card (#6 above).  Unsure if the hole was big enough, we took our 3D print of design #4 and used a dremel tool to cut the square hole (see picture below).  It wasn't pretty, but the hole worked just fine to access the SD card.
The opening to expose the SD card isn't attractive, but it does work.
Final Design.  After all of these iterations, we got to our final design, which is shown below.  The CAD files for this design are shared on the Tympan GitHub here.
Our final design.  Download it from our GitHub!
SLA vs FDM.  We printed a couple of copies of our final design using SLA.  The quality of the translucent SLA prints was fantastic, especially the surface finish.  But, the SLA prints were expensive -- too expensive to make lots of copies.  Luckily, I got hooked up with the good folks at Tangible Creative, who were able to FDM print 10 sets of enclosures for about $10 a set.  They came out pretty nicely (see picture below).  Sorry about the boring black color.  Next time I'll pick something more fun!

Fitting the Tympan electronics into the FDM-printed enclosure.
Make it Pretty!  So, while I ended up with an enclosure that does the job, it has plenty of room for improved aesthetics.  If you think that you can make it better, take our design files and make something better!  Please!