This snippet will tame TinyMCE within Wordpress and prevent it trying to clean up the code and reformat it. Specifically helps to prevent wordpress strip p tags and line-breaks and stops it from inserting nbsp etc

tame-tinymce.php

function mce_mod( $init ) {
  $init['forced_root_block'] = 'p';
  $init['apply_source_formatting'] = false;
  $init['preformatted'] = true;
  $init['force_br_newlines'] = true;
  $init['wpautop'] = false;
  return $init;
}
add_filter('tiny_mce_before_init', 'mce_mod', 99);