I just used 3 clamps I got at Harbor Freight. They are adjustable.
I took the rubbber seal out of the lid and rolled up some tin foil "snakes" to put into the lid's lip instead.
It's not a perfect seal, but after a few smokes, the drippings and just general grease settle in the lip and help seal it up.
I can shut everything down completely and the fire goes out, so it's can't be leaking air very badly.