So the codex documentation does not say anything about this, but digging in wp-includes > nav_menu_template.php found that if you do not specify the theme_location argument for wp_nav_menus() then none of the container / menu style arguments will work. Below I have documented the process for generating a menu with these args, hopefully it will help someone else!
In functions.php:
register_nav_menus( array(
‘primary’ => __( ‘Masthead Navigation’, ‘DLLT’ ),
‘secondary’ => __( ‘Footer Navigation’, ‘DLLT’ ),
) );
In wp-admin, assign pages to the menu just registered, then in my header.php to output the menu I used:
<?php wp_nav_menu( array( ‘menu’ => ‘Masthead Navigation’, ‘container_id’ => ‘Navigation’, ‘theme_location’ => ‘primary’ ) ); ?>
<div id="Navigation" class="menu-masthead-navigation-container">
<ul id="menu-masthead-navigation" class="menu">
<li id="menu-item-23" class="menu-item menu-item-type-post_type">
<a href="/support/">Support</a>
</li>
</ul>
</div>