Here's the official link for the park. It gives lots of good information.
Crater Lake Nat'l ParkThere is a campground in the park and some sites have hookups.
Check on the closing date as it gets a LOT of snow.
If you don't want to stay in the park I would suggest one of these state parks:
Collier Memorial on Hwy 97.
Joseph H. Stewart State Recreation Area on Hwy 62.
Both highways are excellent for RVs. Depends which direction you're coming from. If from I-5, take 62 toward Prospect, OR.
Have a great trip. It's awesome to see!