Is there a way to have a custom template php file that is only used for previews instead of it using the single.php file? This way the user knows they are in preview mode?
1
You could use the conditional is_preview() to add a bit of extra content.
For instance, you could put this at the very top of your single.php right after the header is called – or you could put it in your header.php file if you want it shown at the very top of the page:
<?php
if ( is_preview() ) { ?>
<div>You're viewing a preview</div>
<?php } ?>
Hope this helps, best of luck!