Most of what i've seen (and am using) is fiberglass of ceramic rope gasket attached with a food-grade high temp silicon RTV.
If I recall MSDS (Material Safety Data Sheets) for both fiberglass and ceramic rope gasket indicate it's a mechanical irritant on skin and if ingested for the same reason. Food grade high temp RTV, assuming you stay within the prescribed temp ranges (available up to 650 degrees F, look for "FDA approved for food contact on the label") is just that--fine for food contact and safe at whatever temps are on the label.
There are alternatives such as nomex grill gaskets--I have one on my ceramic cooker and it does a great job. One might also consider straight-up oven gaskets, but I've never tried them. Most of them come with little wires for mechanical attachment, but this might take some extra engineering on a smoker to get affixed (or just RTV it into place).
Hope that helps,
Bb