Hey Todd,
In theory you are correct with the HTTP client protocol. In reality, I did not have any success with that. Everytime i tried to send a message, the process would panic. I ended up writing a tps proc that would translate to XML and then post the result to the webservice. I have this proc on the Outbound TPS of the sending thread. I also wrote a little to handle the server response which was in xml but we changed that to a simple 0 or 1 for ack and nak. I was able to receive the xml message they were sending in response but didnt want to go through parsing it out. If you want, i can share the code i have.
thanks