I highly suggest NOT using it unless you can cover everything inside your case to prevent ANY condensation. Water BAAAAD for components. But otherwise it would be really suhweet! Remember, your heatsink can only be as cold as the air around it.
Close...your heatsink can only be as cold as the DEWPOINT of the air around it. Dewpoint varies with temperature and humidity. As long as you aren't at or below the dewpoint, condensation isn't an issue.