After I put together the enclosure I realized I had cut out the octagonal piece and did not need to. Rather than keep the hole I modeled up this piece.
Its designed to be printed with TPU so it can simply be pushed into place (the flexing allows it to snap in).
I printed with organic supports. Which come off easier than you might imagine. I used a razor blade to start it and some needle nose pliers to take them out. Then I simply pushed the plug in (smaller side first) and it fit like a glove. Pops back out pretty easily as well if I ever need to put in a full vent.
The author marked this model as their own original creation.