I was there three weekends ago, not in my motorhome, but on a motorcycle. Yes we got snowed on, but you won't have that problem in August. The campground is dry camping and looked adequate. We took the half day guided tour and felt it was well worth the price. The next day we did both the North and South rim drives. Get ready for some walking/hiking depending on how far down into the canyon you decided to go. The scenery is awesome. We stayed at the Thunderbird Lodge which although old, was clean, quite and comfortable. It was nice to have the cafeteria on-site so we didn't have to drive into town for food. If you require hook-up camping you will probably have to stay down in Holbrook, AZ and commute up to the Canyon. About an hour + drive.
Hope this helps. Enjoy your trip and stay cool in August!