I am using one from ACS that is simple, covers the entire tube with the velcro in the back to keep it in place. It has been working fine but with a quick glance at their site, did not find it to send you a link.
Mehrdad, is this the one?
http://www.aircraftspruce.com/catalog/pspages/planesights6.php
Mehrdad, is this the one?
http://www.aircraftspruce.com/catalog/pspages/planesights6.php