Just wanted to say thank you to Russ and everyone else who helped me plan our trip! We did end up spending like 4 nights along the Rhine!
We stayed in Boppard which was a great choice - we visited Koblenz, St Goar and a bunch of other little towns along there and I think Boppard was by far the best choice as a base! We stayed at Hotel Bellevue ... no AC and it was fairly hot, but survivable!
First day we went up to Koblenz. Next day we took the train down to Bingen and took the boat back up to Boppard. The next day we rented bikes and rode Boppard to Oberwesel and back with some stops.
Thanks for all the advice!
Kim