Thanks for your advice!
I think we will probably try the trip up the Coventry. I did notice the railway running pretty close for much of the journey, but looks like its not much of an issue. It's a part of the system we have not visited before.
Maybe a quick visit up the Ashby canal on the way back down if time permits.
Mind you, after saying that, we'll probably end up in Fenny Compton!!
Could always just wait and see which way the boat is pointing when we pick it up!