Answer to this question actually comes from @TomJNowell. Instead of using MySQL calls, use the native functions included with WordPress:

    update_post_meta ( $post->ID , 'forum_id', $thread_id );

where the `forum_id` is the key and the `$thread_id` is the value. I tried `add_post_meta` but that created duplicates. 

To retrieve the meta data

`$thread_id = get_post_custom_values( 'thread_id', $post->ID);`

Now I'm looking at ways to add to the comment meta. Hopefully this helps someone else.