Yes there is. You have to pay for each night per vehicle. Yiu can either pay when they are open or self pay if not manned
There's plenty of parking near the park office (in my experience at least). I don't know about leaving a vehicle there overnight, but I guess that's what people do when they camp. Best to call them.
You can reserve a spot in the campgrounds, but you will need to plan far in advance. I do not know how the rangers feel about randomly parked RV in the parking lot. This is for the Morgan Hill entry. I do not know about the other entrances.
They have some camp spots that can accommodate small RV's
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