Remove port from ServerName, this in conjunction with setting UseCanonicalName to on allows redirect URLs to be generated without the backend port in them.  Added rewrite module.  Changed proxying to use mod_rewrite.  It now checks if a PHP file exists in the application directory first.  If that file exists then it proxies it.  It also handles directories better.  If a directory is requested, it looks for index.html and if that doesn't exist then index.php.