I'm having trouble creating a custom post template in WordPress Gantry. Perhaps this post will save someone else some aggravation.
I've learned a couple of things.
CustomPress will not create a custom post type for Gantry in Word Press because the single.php file is stored in a subdirectory of wp-content even if permissions are set correctly to 777 and php in is safe mode off. CP is looking in wp-content not wp-content/html for the file single.php
If I manually create the file single-custom_name.php by copying it still does not seem to be used. I can tell this by modifying single.php and single-custom_template.php to have different text in them. And Gantry only seems to use the single.php file.
In Gantry all overrides and customization happens in the Themes/Widgets area.
Once you create a new override there you can switch to Gantry Setting and the the Assignments tab to choose when you want to override the single.php setting. Then if you go back to widgets you can copy code out of single.php and put it in the widgets where you want it.
So for good developer recordkeeping I recommend manually creating a copy of single.php to single-custom_template.php and then inserting comment lines in the new file to show what code got copied out to Gantry widgets and you are expecting the code in the widgets to override.
All that said, I like the CustomPress plugin because it allows me to create posttypes, custom taxonomies, and custom fields all with one plugin. And I can use the posttype in the gantry override without having to remember to code a category or tag everytime.
Hope this helps someone else. I've stopped pulling my hair out now.