What about the carbs in milk? 1 cup of skim milk has something like 12 grams of carbs in it, I don't know about chocolate milk but I can only assume it is higher. Sounds like a pretty bad idea. Even the low fat chocolate milks I have seen contain sat fats.
The best pre-sleep meal I have ever seen is a whey shake with Udo's/flax (slows digestion of proteins) and a bit of cottage cheese. Cottage cheese is where it's at especially if you can get the stuff with low fat and low carb content.
EIDT:
I wasn't aware that casein protien had any effect on insulin suppresseion but rather the digestion of protein, do you have something on that? I'd be interested to see.