Recommendation on where to add routine for adding meta boxes

First off, really love this boilerplate, so thanks for putting it together. I'm using it to restructure an existing, functional plugin that has front-end and admin modifications. One such piece is adding meta boxes to the add/edit page of a custom post type. Where would you recommend adding the routines for this as a matter of best practice? A private method in class-plugin-name-admin.php that is called in the constructor? A public method in the same class that is called (like the enqueue* methods) by Plugin_Name::define_admin_hooks (class-plugin-name.php)?