You can also learn about how special and visual effects were used to make characters fly, and all of the magical creatures seem real. After spending a few hours at Hogwarts, you can see what else Watford has to offer by exploring Bhaktivedanta Manor or Cheslyn House and Gardens.
While it can be difficult to find campsites near London, once you get to the northern half of Hertfordshire, there are many places to park your motorhome hire overnight.
The Hertford Camping and Caravanning Club site has great reviews. Why not visit their site for a night or two.