Nice looking mod!
I think that looks so slick!
From all that I've seen, you will really love the drum smoker. Way longer cooking with less effort and no refueling.
It gets me thinking that maybe we can sit the whole weber atop a drum which would seal the drum...mmm well, maybe not.
For sure you want to remove the rubber gasket. I think that a bead of high temp silicone might be useful in its place, but maybe it is not even needed.