Here is the general rule - External enclosure must be metal, where is steel or aluminum. It just for the heat withdraw from the HDD, so you can have a reliable storage.
USB2.0 is too slow... If you can look at this enclosure. http://www.datoptic.com/esata-usb3-usb2-fw400-fw800-sata-enclosure.html
It is not cheap but I'm very happy with it.