Custom Post Type Metabox

Has anyone tried creating a metabox in for custom post types?
I assume it’s something like this but the callback must not be right because the meta box is there but no html is being displayed in it

add_action( 'add_meta_boxes', 'add_job_openings_metabox' );
function add_job_openings_metabox() {

	add_meta_box( 'pt_post_templates', 'Single Post Templates', notsurewhattoputhere , 'job_listing', 'side', 'default' );
}

and I do have this in my register post type variables
'register_meta_box_cb' => 'add_job_openings_metabox'

http://wordpress.org/plugins/single-post-template/