Adding a hinge to the lid of your Weber Smokey Mountain is an invaluable tool!
The clever folks at Team Unknown got tired of looking for a place to put their hot lid, so they built a stainless steel hinge.
Of course everybody who saw it wanted one so now the sell them. It has a clever little latch so when you open the lid it stays open and won't slam on your head when you stick it in there to smell your meat, and a pin that you can remove so you can take the lid off all the way. The pin has a bearing that prevents it from coming out accidentally. Mounting it took 15 minutes. The only problem? I needed to buy a new cover because the old one won't fit over the hinge.
While you're putting on a hinge, why not get better control over airflow? You can buy a Nomex gasket kit that seals the lid, the base, and the side door. Nomex is rated to handle temps up to 572°F, and it is held in place by RTV silicone rated up to 650°F.
Here's a kit with the hinge and the gaskets that will fit all sizes of WSM. I have both and they work. There is a minor problem. The hinge sticks out so far that you cannot fit the standard rain cover over the WSM without cutting a slit up the side. It is not a problem on the Kettle because the lid hangs over the bottom half, but on the WSM the lid fits into a lip on the bottom half and if you don't use a cover water will get in. Hence the silver medal.