I will second San Simeon State Park. I have stayed there a couple of times. If it is open, I prefer the upper section on the left as you drive into the park before you head down the hill. I have stayed here a few times over the last few years.
Please make time to go to Hearst Castle just up the road. They have plenty of parking for any size vehicle at the castle. It is a must see and only a mile up the road from San Simeon State Park.
There is a great seal watching area just north of the castle as well. Large dirt parking lot for any size RV and free.