Hillbilly Jim: Another thermometer nerd! Yeah, baby! :)
I've cold smoked cheese a number of times with the AMNPS in my MES-40 (which is smaller than yours, and insulated, too). The temperatures stayed just fine, but I have always done it when it was cold outside. Once, it was -20 for most of the smoke. I had to manually cycle the heater in the smoker on periodically to keep the temperature high enough (I like it around 60 degrees).
You can't set the controller on my MES-40 that low. Modifications may be in order. ;)
But at ambient temperatures near 30 or 40, just the heat of the AMNPS burning the pellets kept the smoker at a nicer, higher temp. So it probably is a matter of the size, insulation, and airflow, too, that determines whether or not the AMNPS's heat is enough to raise the smoker's internal temp.
Since it is usually very dry here in the winter, the pellets have burned nicely for me during those cold smokes in winter.
But I would like to be able to do cold smoking in summertime, too. So a mailbox mod of some sort may be in my future.
Not to derail this thread, but I've been a real temperature control nut for many years. Have you seen the Reference Thermapen?
I recommend it highly as an affordable calibration thermometer.
Cold smoking in Summer----Fill a couple jugs 3/4 full with water & keep in freezer for such occasions. Frozen water in jugs won't add humidity to smoker like Ice in a pan does.