Scroll to the post with the white truck, these are what i have. http://www.dieselplace.com/forum/76-gm-trucks/127-3500-dually-trucks/440527-dually-rear-mud-guards.html
I bought the factory ones for mine. They fit, look good and do the job. After a whole bunch of 70 + mph trips down gravel roads the flaps are still there so they are tuff too.
Is your camper a 5th wheel?. If so check out the hitch mud flaps. They attach to your lower tow hitch, if you have one. They can be adjusted to any width & also removeable when not towing. Some are called Rock Tamers. Good luck.