I have installed and activated the plugin and created a custom template. I have assigned the custom template to a particular post and can see the custom field that was created on the post.
However, the single.php template is being applied rather than my custom template.
my custom template file name is trails_single.php.
At the top of the file I have:
<?php /* Template Name Posts: trails_single */ ?>
The remainder of the file is a copy of my single.php code with the addition of an echo statement to let me know which template I'm actually looking at.