do you have a website? does it have the appropriate backend programing to be one of the first hits when a search is done for a campground in the area you are located?
are you overpriced for the area you are in? realizing your description of the type are park you built, it is still possible to be over priced.
another idea. we crossed paths with a campground at a RV show. it is primaraly a seasonal campground, and is under new ownership. the new owners made several changes and were over open with their promotion of what they have changed and what they have kept. one thing they added was a "day fee" so someone or a family could make their campground a day trip. they had a pool and may other activities that could be enjoyed by a day visitor. this is a great way for someone to tryout your campground prior to deciding to becoming seasonal.