How to design the layout of the "Single Post" page?

Hey Bob!

Try adding this at the very end of your theme functions.php file:

function activate_alb_posts($boxes)
{
	$boxes[] = array( 'title' =>__('Avia Layout Builder','avia_framework' ), 'id'=>'avia_builder', 'page'=>array('portfolio','page','post'), 'context'=>'normal', 'expandable'=>true );
	$boxes[] = array( 'title' =>__('Layout','avia_framework' ), 'id'=>'layout', 'page'=>array('portfolio','page','post'), 'context'=>'side', 'priority'=>'low');
	
	return $boxes;
}
add_filter('avf_builder_boxes', 'activate_alb_posts');

Cheers!
Josue