Hi pcarlson,
I have different printer (Bukito), but I decided to try your file. I have my shells set 1o 1, but due to the thinness of the walls, they're basically just an inner and outer shell.I observed the same thing that you did (doing the inner wall in one direction and the outer wall in the other diretion. However I couldn't see any gaps like you saw. I tried with 0.1, 0.2, and 0.3mm layer heights.
Here's a photo of all 3:
I noticed that your beads seem a little more well defined. I was using PLA at a temp of 210C. I'm also rather new to this, so I find these discussions fascinating.
I would think that perhaps you want to increase the temperature a bit? Or perhaps reduce the retraction? I have my printer (with a Bowden tube) set to 2mm retraction @ 2400 mm/min