I have a different carrier which I really like. It has a cross brace (from tow loop to tow loop) which stops it sagging and squeaking, which apparently can be an issue with the SMA carrier. It also has a grease zerk fitting for easy lubrication and a lockable handle. I purchased with my truck new (as an option), but I see the same one is available here with installation instruction:
http://www.premierhummer.com/hummer_...e_carrier.html
Mark.