I'm asking this because I'm running into a little problem, finding a hotel in Rudesheim on the night of a Rhine A Flame cruise. I thought 4 months was early enough to start looking, but I was wrong. Everyone is booked or requires more than one night stay.
I'm now looking at a nearby town. I don't want to go too far away because of the late hour the cruise ends.
So, my tip: book very early if there is some festival/event of any kind in the area, probably more than 8 or 9 months if possible.