Camping right at Crater Lake is very limited (and in my opinion, not as nice as some of the other campgrounds in the area). I would recommend that you check out a few of the other campgrounds that are in the area, and perhaps plan a day trip to Crater Lake.
We love the campground at Odell Lake (forest service campground on the east end of the lake). It is right on the shore of the lake, so has beautiful lake view, but is small enough so that you aren't parked in middle of parking lot. It also has the advantage of being right across the creek from the Odell Lake Lodge, which offers boat rental, canoe rental, and a very nice restaurant.
I would also recommend the Lake of the Woods Resort, which is south of Crater Lake.
Another area of Oregon, as long as your in the neighborhood, which is worth the trip is the Lava Beds on McKenzie Pass (check with rangers to see whether or not motorhome you rent will handle the road as it is fairly narrow and windy). The Metolius River at Camp Sherman (just west of Sisters, Oregon) has some excellent campgounds and fishing on the Metolius is wonderful (but is catch and release so buy hot dogs!).
The Wildlife Safari at Roseburg Oregon is certainly worth the trip. And - if you don't mind boondocking (no hookups) there is a very nice campgrounds affiliated with the park. I believe that they charge a marginal fee, but almost always space available.
You will find that Oregon State Parks are perhaps some of the nicest you will ever run across. Most offer full hookups, nice showers, and are very clean and well maintained. One of the best is Silver Falls State Park which is on Highway 22, about 20 miles east of Salem, Oregon. The park is large with a great variety of sites. There are miles and miles of hiking trails, and if memory serves 7 falls which are beautiful to see. Just east of there are the Oregon Gardens which are absolutely beautiful!
One of the best things about Oregon is the abundance of parks and campgrounds, and inland you can almost always find campsites, however, if you are headed toward the coast on summer weekends, I really recommend reservations in advance - they fill up very quickly.