That acurite should be IN the tank on the cool side 3-5" above the substrate. Mount it on the glass with some double side sticky pads. Also, I hope you live somewhere humid because an open top like that isn't going to work very well for him. That and he could get out on you one day...

If he's eating like you say though and his sheds are all 1 piece he's probably doing ok now, that is a much better setup than I had up until very recently.