In the end I didn't really use the bench and instead generally masked it using the people. I was able to get the tree in some shots, but due to the cloudy day, it was VERY dark beneath it's canopy. So I just used it as background interest. I was lucky - the rain eased off for an hours just as the ceremony ended so I was able to get the formals shot in the church grounds.
I am quite happy with the results. Full write up and critique request here: http://www.apug.org/forums/forum292/...ml#post1018083
Thanks to all of you for your help with this one - I learned a lot from the discussion.