I can see smoke escape from around the door, and one side of the lid (the side that had the cables fro the probes on it) but even then it was only a little. I have ordered the nomex gasket kit too.
IMO what you see leaking out (the smoke) is not the real problem. That is excess air leaking
in.
When my 18.5 WSM (47 metric) was new I could close all the vents and it would hold about 250°F (121°C) until the charcoal burned to ash. I fixed this by running a bead of high temperature silicone around the groove at the bottom edge of the middle section.
After a few smokes, sufficient residue will build up and help seal these joints.
I would not run thermometer probes under the lid as that can damage them. I use a cheap hardware store grommet.
(After I did this one, I figured out that one grommet is sufficient.
)
Water in the pan is a big help while you get the hang of precise temperature control. I used that for years. Now I usually foil the pan because I have learned how to get the temperature where I want it. I have also come to realize that holding 225 vs 250 or even 275 just isn't that important. All will produce good results sooner or later.