Very nice!!
If this is not stickied in the DIY section, it probably should be. By far the nicest DIY cooler build I have seen
The only thing I would be cautious about is the AC fan. Inherently AC fans create heat. Great if yours does not generate much heat, but I suspect that is why both your probes read over the setting of the Herpstat.
I'd be curious to see what your temps would read if you just kicked off the Herpstat for a day? You may be surprised.