I use the large chimney for the Slow-N-Sear. It will buy you more time, but I don’t think you would get 10 hours out of it.
I am a big fan of the Slow-N-Sear for things like thick steaks that require both a high heat to sear and a low heat to cook. But I found that the snake method is better for low and slow cooks.
To do low-and-slow with the Slow-N-Sear the bottom vent is almost closed and the top vent is partially closed as well. This low airflow caused a creosote buildup in my kettle that was starting to make the food slightly bitter. The buildup under the top vent made it difficult to adjust after a while.
The snake method is more fuel efficient and will usually get you in the proper pit temperature range with the vents wide open, which means you get good airflow, clean smoke, are not chasing temps, and are not getting creosote buildup in the kettle.
A two wide by two high row of charcoals will usually get you close to the proper smoking temp. If it is cold a third row of 1 wide will usually bring it in range. You just need to get it in the proper temperature range, it doesn’t have to be an exact number.