I would say a 40g is way to big for a juvi. I would only put a very large female in a 30gallon long tank.

If he doesn't eat for you, I would think about sectioning off part of the 40g tank.

Hiding is very normal. I only see mine out and about on feeding day when they can smell the rodents. If you bought the little guy as a display snake, well I am sorry to be the bringer of bad news...