Stephanie - get a copy of the "Good Sam Travel Guide and RV Park Directory". It's a massive book that lists most campgrounds, and in each campground listing, it will itemize any pet restrictions (if they have them at all) according to (S)=size, (B)=breed, or (Q)= quantity. The first two, if listed, might make you want to call the campground for clarification.
My experience, traveling with 3 dogs, 2 of them largish, was that we never had a problem finding a place to stay. And my experience camping near folks with Dobies is that the ones who are traveling tend to be extremely well-trained!