If you want to use an internal hard drive as an external drive and need a ultra-affordable protective casing, then check the ProtectaDrive Silicone Sleeve for 3.5" Hard Drives from Newer Technology. This casing is made of a lightweight, flexible silicone rubber and can protect your 3.5" hard drive against shock, short circuits, and static electricity. You will need to separately purchase a drive adapter for connection to your computer.
This sleeve features an open top area to allow the drive to cool
The sleeve is made of a molded, flexible silicone rubber that offers production against static and sudden impacts. It is non-conductive