Chris,
Thank you, I'll have a go with the airmail over the weekend and see how I get on. I thought there was probably a good reason why no module seems to include the ability to be configured the way I described, like life, things are never as simple as they seem.
It wasn't in any way a criticism of your work, this is the first shipping module I've tried that I've been happy with and its obvious that you've put a lot of work into this so thanks again.