Each of the Previews in your Tugboat project count toward the total storage space available in your project’s billing tier. By default, Tugboat is configured to automatically delete Previews when their corresponding git pull requests are merged or closed.
If you want to change the setting to automatically delete Previews when their PRs are merged or closed:
Go to username -> My Projects at the upper-right of the Tugboat screen.
Select the project where you want to configure auto-delete settings for Previews.
Click into Settings for the repository.
Click the checkbox to change the setting.
Press the Save Configuration button to save your changes.