There is a simple way to keep your trailing slash settings consistent without having to install extra plugins. Most WordPress users and developers are unaware that the trailing slash mode is determined by whether a slash appears at the end of the "Custom Sturcture" field.
You may easily adjust it using the built-in permalink settings. Even users who are unfamiliar with WordPress should find this simple. To do so, go to the "Settings -> Permalinks" section and, depending on your situation, either add or delete the last slash.