A couple of tips...from someone who has built two bators out of the same type of cooler that you have there.
Did you cut some ventiliation holes? In my cooler bator, I have vent holes - about 5-6 of them, 1/4" around the bottom of the bator and a couple of large (3/4=1") holes at the top for humidity control. I just cover them with duct tape and open and cover as needed
Lastly, I found that when you up the humidity, water will condense on the glass at the top and then run down into the open spaces left in the lid where i cut my hole out. Then you get a lot of water collecting inside the lid, which makes it hard to keep the humidity steady, AND probably is a breeding ground for the nasties when you have it stored between uses. I covered the gaps with duct tape too and that solved that problem.
One final thought.... With the thermostat inside the outlet box, how are you going to be able to adjust it as needed? Getting those thermostats regulated is a tedious process of nudging and bumping it this way and that and then waiting a few hours before you check again... I also found that if the air flow is not good around the thermostat, the temps fluctuate even more wider range than if there is good air flow around it.
EDIT: I went back and see that you have a hole drilled to adjust the temp.
Just my thoughts from building my cooler bators...