Just past the gates of the Namib-Naukluft national Park is the Sossuvlei campsite. It's pretty big, and has a swimming pool (open in summer only), individual taps and some bathroom booths with hot water. If there is no room for this task, they often make a hole between the bathrooms and the pool. They also have individual barbecues available. The park gates open at 5:00 and I recommend you get up early because a queue forms. ;)
This complex, located in Rohobot about 100km from Windhoek, is essentially a great place to spend the weekend with family or friends. There are many water activities and a "port" where some leave their boats. The atmosphere is very family friendly and festive. During the weekend, most of the camping places are taken but if you want to spend the night there many of the guests vacate after 6pm, so if you wait you may get lucky.