Use this snippet to have the weight of composited products added to the container weight when the Non-Bundled Shipping option is unchecked.

woocommerce-composites-variable-container-weight.php

<?php
/**
 * Plugin Name: WooCommerce Composite Products - Variable Container Weight
 * Plugin URI: http://woocommerce.com/products/composite-products/
 * Description: Use this snippet to have the weight of composited products added to the container weight when the Non-Bundled Shipping option is unchecked.
 * Version: 1.0
 * Author: SomewhereWarm
 * Author URI: http://somewherewarm.gr/
 * Developer: Manos Psychogyiopoulos
 *
 * Requires at least: 3.8
 * Tested up to: 4.8
 *
 * Copyright: © 2015 Manos Psychogyiopoulos (psyx@somewherewarm.gr).
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */
 
// To use this snippet, download this file into your plugins directory and activate it, or copy the code under this line into the functions.php file of your (child) theme.
 
add_filter( 'woocommerce_composited_product_has_bundled_weight', 'wc_cp_bundled_weight', 10, 4 );

function wc_cp_bundled_weight( $has_bundled_weight, $product, $component_id, $composite ) {
	return true;
}