Adding a checkbox for a custom field

I'm modifying a form that adds a new place in kolimarfy's places extension.  This code does create a checkbox, but the value isn't being saved.  The underlying column is tinyint(1).

    'pl_permit' => array (

                'label' => 'Places Permit',
                'type' => 'checkbox',
                'required' => 1,
                'attrs' => array(
                 'checked' => 'unchecked',),
                'db' => 'pl_permit',
                'view' => 1,   
            )

thanks for any assistance!