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I used these for my smoker build. Got them at Tractor Supply for a little over 5 bucks each. They're a pretty sturdy over-center latch. I burned mine during one of my barrel burns to remove the plating, then sprayed them with hi-temp paint after I welded them on.
On all my builds I use round bar stock on the door latch. I try to get a picture later for you. Bend the handle section 90 degree and use washers on the inside and outside of the door to position the handle. You can put a spring on the inside under the washer that will hold the handle straight. I don't I try to get the washers in straight and tight enough. Then on the inside i use another short piece of bar stock welded to the piece going thru the door at another 90. So when you move the handle up or down the part inside does the same. To lock the handle down i weld a piece of 3/4"angle against the wall so the the bar stock catches the edge of it. Weld it on a small angel so the when you close the handle it actually pulls the door close.
Hexobular has a good choice,weld or screw on;with a little gasket material on the Smoker surace and some Vasoline on the door,just shut it over night.does great as a seal