Check out this care sheet.
http://www.redtailboas.com/general_c...eral_care.html

You really need to get his temps up. He is showing the first sign of respiratory infection, and his immune system can't handle it at low temps.

You need to get him out of the critter keeper, out of the corn's cage, and into his own. You risk passing on any infection to the corn snake.

Corn snakes are able to live in temperate climates, boas are tropical.

I would hope you take him to a vet as soon as possible.