They make "food grade" high temp. RTV. It can be hard to find though.
I just used regular Permatex high temp. RTV to seal the chimney and all the holes to include sealing the rope gasket to the doors. If you are careful and use very little it is fine. If you look at the design of the doors, it will make sense and is not dangerous in any way. The way I sealed mine up, there is no RTV visible anywhere inside the smoker. A tiny bit of that stuff goes a long way!
The stuff that comes in those kits does not stick to the paint on the smoker doors and it will wind up making your gaskets hard. That stuff also does not hold the gasket "in place" like RTV can. So, as soon as you get the gasket in position, it will slide off. If you decide to use it, you will see what I mean.