ok, first of all the iframe html in not well formatted, html, head, body tags is missing
A part this, you are not inserting the javascripts:
<script type='text/javascript' src='https://www.google.com/jsapi?ver=3.2.1'></script>
<script type='text/javascript'>
google.load('visualization', '1', {'packages':['corechart']});
google.load("maps", "3", {other_params: 'sensor=false'});
</script>
<script type='text/javascript' src='https://www.bicycletouringhub.com/wp-content/plugins/wp-gpx-maps/WP-GPX-Maps.js'></script>
[Please post code or markup snippets between backticks or use the code button.]
the temp file name is a little bug, you can wait the next release or delete this row: “print_r($gpx);”, row number 100 in wp-gpx-maps.php
