We have stayed at a few RV Parks in the area.
Depending on what you plan to do and see while you visit.
I can recommend Huntington beach, (Bolsa Chica State Beach Campground), it is literally a parking lot right on the beach. However quite nice and centrally located, just a little pricy. Huntington Beach Camping - RV Campgrounds
Closer to Disneyland is (Anaheim Harbor RV Park). 2 minutes to Disney, 36 miles and 57 minutes to Pasadena. They do not have a limitation on the year of your RV like some RV Parks in the area. Very clean, and so close to Disneyland that you get fireworks everynight
We also liked, (Orangeland RV Park) very much, Clean and quiet, the park used to be a citrus grove and you are welcomed to walk around and pick fresh oranges, grapefruit, etc. It is just across the creek from Angels Stadium if you want to plan a game or just around the corner from the Honda Center for concerts and other events. Yet still close enough to everything else.