Common Boa and humidity

[Saml8]

I just picked up a baby boa (about 9mos old) at a reptile show here in Denver Colorado. Can anybody give me some suggestions of how you keep the humidity up in a really dry climate like Colorado? I don't plan on keeping him in a plastic tub but rather a glass terrarium (at least while he's smaller). We have corn snakes which do pretty good with the dryer climate. And when I see them going into shed I put a moist hide in the terrarium.
Thanks in advance for the help!