I just put a short bolt and nut thru the holes. Sealed them up very well.
I have been wrong many, many times, but I think your problem will be with controling draft. My lid does not seal at all, and I have no problems.
Looking at your pictures with the "stack" it looks to me like you will be getting an excellent draw up thru that pipe. If I am right, you need to be able to control the bottom end on the intake side.