Why is my custom theme template not found?
Try something like this:

function mytheme_preprocess_page(&amp;$variables, $hook) {
  $variables['theme_hook_suggestions'][] = 'custombody';
}


to add a theme hook suggestion a template called 'custombody.tpl.php'.

However it sounds like what you really want to do might be to render the $body directly, before it gets passed to the default template. In that case you'd use a process or preprocess function to do that directly instead of doing it in the template itself.