Instead of water, I would substitute a pan of moist sand. A loaf pan should do. My Amerique is stable. I did check it against a Williams-Sonoma (Maverick) last year out of shear boredom after reading about the significant differences with the maverick and other smokers and there were some differences. I attached the remote probe adjacent to the sensor in the Amerique. However, I was getting great food so I put the Maverick away and ceased my worries. On my first butt, when it was at 195 degrees internal, I checked it with a thermapen and was within 1 or 2 degrees of what the on board system read. And I probed it in a couple of areas. Overall, very satisfied. Something else to consider is the way the Amerique and the Maverick (or any sensor) processes the temperature. Is it taking a reading or several and processing an average through a built in algorithm?
Smoke leakage: it will eventually seal up. Maybe not 100% but it will diminish over time. Whether it exits the vent or at a corner or top of the door, it has to go somewhere. An inexpensive set of brass gauges should show you the gap and if you feel the need, some 3M high temp stainless steel tape cut to size will lessen or eliminate the gap.
I tell a lot of people two things: 1- nothing made by man will be 100% perfect and 2- if the food is good and on time, results trump all else.
The folks at CS will be able to help, and some of the forum members may have some thoughts on this issue.