First of all, welcome to the site!

Your little guy is cranky because he's scared and baby rainbow boas can be very shy and defensive. He definitely needs something a lot smaller than a 40 gallon right now, and while I would recommend switching to a tub since they hold humidity much better, you can make the tank work. You can get more fake plants and branches (rainbow boas like something to climb on) to clutter it up and help him feel more secure. You also might want to get another, smaller hide, as the half log one might not be enough. And if you decide to keep using the tank, I would switch to an under tank heating pad with a thermostat instead of the light and cover most of the top with aluminum foil to help hold in the humidity.

I would wait a couple more days before trying to feed him, and you should try feeding him in the tank too. That's how I feed all of my snakes (including my rainbow) and I've never had a problem. It's much less stressful for both you and the snake

The care sheet here is very helpful if you have any more questions: http://ball-pythons.net/forums/showt...es-cenchria%29 Basically, they like lower temperatures and high humidity.