So, you have a template named "mytemplate" and you want it to show in the footer? You still have no preregistered the variable $showdata, or the results from your created template, for use in the footer template. You'll need something like:
PHP Code:
vB_Template::preRegister('footer', array('showdata' => $showdata));
You'll need to do that for any variable you want to use in the footer. (Right now the results of your created template are not assigned to any variable.)