I use both of these web base sites. They are free all you need to do is added them to your bookmakers.
http://www.campgroundreviews.com/
This site list if the park is big rig friendly and what services the park offers. Web link to the campground is provided also. You can also rate your experiences at the park and offer your comments on that park.
For federal parks such as Forest Service or COE parks, I use this site.
http://www.recreation.gov/welcome.do?topTabIndex=Home
This will also tell you if your camper will fit in the camp sire and what services are offered at the park.
Jim