Adding trailing by yourself is not solution. because if i forgot to add the trailing the page would come up with page not found which is not good for seo.
Custom Permalink was one of the most popular plugin but due to some reason it is unable to provide the services and support anymore.
So, I have created a fork of custom permalink with the name of Permalinks Customizer. In this fork, i have fixed issues(as much as i know) and provided some new features. Maybe it helps the users ??
If you want to have some solution by which you don’t need to add trailing slash so, try this plugin. Hopefully it resolve your issue and make your life easy.
You can download this plugin from wordpress as well as my github repository.
1. https://www.ads-software.com/plugins/permalinks-customizer/
2. https://github.com/yasglobalinc/permalinks-customizer/