mxbuilder wordpress custom page template

mxbuilder_rss.php

<?php
/*
Template Name: mxbuilder custom rss feed
*/

$numposts = 10;

function mxbuilder_format_date($timestamp = null) {
  $timestamp = ($timestamp == null) ? time() : $timestamp;
  return date(DATE_RSS, $timestamp);
} // mxbuilder_format_date

$cat = (isset($_REQUEST['custom_cat'])) ? $_REQUEST['custom_cat'] : "";
$posts = query_posts('showposts=' . $numposts . '&cat=' . $cat);
$lastpost = $numposts - 1;

header("Content-Type: application/rss+xml; charset=UTF-8");
echo '<?xml version="1.0"?>';
?><rss version="2.0">
<channel>
    <title></title>
    <link></link>
    <description>Latest posts</description>
    <language>en-us</language>
    <pubDate><?php mxbuilder_format_date(strtotime($ps[$lastpost]->post_date_gmt)); ?></pubDate>
    <lastBuildDate><?php mxbuilder_format_date(strtotime($ps[$lastpost]->post_date_gmt)); ?></lastBuildDate>
    <managingEditor></managingEditor>
<?php foreach ($posts as $post) { ?>
    <item>
        <title><?php echo get_the_title($post->ID); ?></title>
        <link><?php echo get_permalink($post->ID); ?></link>
        <description><?php echo '<![CDATA[' . apply_filters("the_content", $post->post_content) . ']]>';  ?></description>
        <pubDate><?php echo mxbuilder_format_date(strtotime($post->post_date_gmt)); ?></pubDate>
        <guid><?php echo get_permalink($post->ID); ?></guid>
    </item>
<?php } ?>
</channel>
</rss>