The shower house in the camp grounds is for registered campers. They allow our trail workers to use them on our volunteer weekends, but they should not be viewed as shower facilities for non camping park users. The main issue is capacity in the summer. They may not enforce to much in the off season, but they do enforce in the summer.
The best way to shower in the summer is to use the pool which costs $3. Take a shower and a dip in the pool to cool off.
Whether you are camping or using the pool showers, please be respectful of the park staff who have to clean the facilities. Please do not go in covered in mud and especially do not take your bike into the showers to clean (yes people have done this). Basically make sure that shower is left in good order when you are done.