Is it possible to host a WCF service in IIS, access it over HTTP and have the message body encrypted using a wsHttpBinding configuration?
Yes, any protocol that can support message security and the WS-Security standard will be capable of encrypting your messages - it's actually the default setting, too.
See Message Security in WCF for more information, and for hints about how to secure your messages using a Windows credential or a X.509 certificate as the "shared secret" between client and server to ensure encryption.