The plugin is working perfectly, but I do have one feature request. Right now a css class gets added when using a custom post template, but nothing gets added when the default template is used. This makes it very hard to target ONLY the default template in css without completely changing all the classes on the page.
Maybe add a "post-template-single-php" class on default posts? It should only take 1 extra line in the body_class function (line 85) in custom-post-templates.php .
Thanks for this great plugin!