Boy! Keeping up with timely posts is harder than I thought!!
I've now made a total of 8 snuglets. Along the way, I experimented with different ways to get the corners done so that they 1) look nice and 2) aren't terribly thick to sew through.I think I finally have it, although it took me a few tries to get there.
Here's a rundown of the progression:
Snuglet #2: At first I tried a mitering technique that's in the Reader's Digest New Complete Guide to Sewing. The mitering part worked just fine. However, their technique, as written, didn't allow me to double fold the edges - they were folded once only. Since I had gotten in my head that I wanted the raw edges bound, this wasn't going to work. (And I'll be the first to admit that I'm probably being overly picky about the whole raw edge thing).
The corners on this one ended up being sort of mitered because I had to cut the one of the corners to do the experiment. I cut each of the corners, then folded the edges twice. The result was that the corners fit nicely, but with a bit of a gap in the corner where one fold met the other fold. This as opposed to the nicely sewn corner that the original mitering technique would have given. To fix this, I stitched the two edges together and in such a way that it showed on the right side.
All in all, not perfect, but doable.
Snuglet #3: With this one, I set aside the mitering idea and played with cutting out some of the corner so that they could be folded without overlapping in the corners. This idea mostly worked. However, it also had a gap in the corner area that had to be sewn up.
Snuglet #4: I went back to the mitering idea but this time, tried to come up with a way where I could get the mitered corner sewn nicely AND get the edges double folded. And HEY! I figured it out! In short, the way to do it is to partially sew up the corner, then leave the rest to be folded under.