I just spoke with the owner of the campground, and he didn't blink when I mentioned hammocks. There is currently a winter discount in effect...the fee schedule is based on tents, of course, but as close as I can tell, it should run about $6/person/night. There is a pavilion available, should the weather turn really snotty. I asked about river levels, and he said it changes from day to day, but that's true anywhere.
I will bring plenty of firewood and coffee...we'll work out Saturday night's meal when we get some idea how many will attend.
What am I forgetting?