The National Park Service sometimes seems to hide information on their campgrounds (the majority of which have no hook-ups), but usually you can find them on the park websites with enough persistence. Try:
We did the Halls Crossing ferry some years ago and didn't camp there, but there did seem to be a nice campground near the ferry landing.
It requires a somewhat more advanced search, but try finding BLM campgrounds in the area. Can't think of any off-hand, but these are well off the beaten track. Some we wouldn't take our Airstream to get to, though.
Have a wonderful trip! Are you boaters?