When trying to merge the vertices in the periscope, I first tried to do it with the full model at once. Being lazy and not wanting to hit the A key, I clicked join doubles, checking the “unselected” option. All of my vertices merged fine except 2. I turned the Merge distance up, but my model started crumpling before those vertices merged. Exasperated, I went back and merged the points individually. After seeing the solution, I realized what had gone wrong: I had an edge selected, and the unselected option merged ONLY the unselected points. The merge was working exactly like it was supposed to!