Crater Lake National Park?

This is what I would do and have done.
Tucson to Banning CA KOA for the night
Banning to Jalama Beach County Park two nights
Moss Landing KOA 2 nights with whale watching the second day
Moss Landing to Willits CA KOA overnight
Willits to Oceanside Beach Front RV Resort Charleston OR two nights
Oceanside to Collier Memorial State Park two nights with Crater Lake on the second day
Collier to Reno NV overnight
Reno to Kingman AZ overnight
Kingman to Tucson
If you have the time add a two nights at Lake Tahoe instead of overnight in Reno.

You also mentioned that you like to hike....
Of course, Mt. Rainer is a big time hiker's destination... short or all the way to the summit (which is a major league distance and altitude trek). But, not a lot of good camping options.

or

Mt. St. Helens for hiking also. You can wander around that area on great trails for hours and hours and days. Good camping options.

We stayed at the Diamond Lake RV Park (private, commercial) and enjoyed it.

At least an overnight for a visit to Crater Lake, two night better. We stayed two nights. We drove out the afternoon of arrival and then the next morning all the way around the rim. The water was perfectly still on that morning visit, hence perfect reflections.

If you are coming up I-5 we have stayed at Seven Feathers Casino RV park and then Day Trip to Crater and Diamond Lake. that is about a hour and half drive to Crater. We have then driven from Crater to Enumclaw, WA and stayed at the Fair Grounds RV park. Then Day trip from there to Rainer, Seattle and surrounding areas. Beach area I would suggest Florence OR and Lane County Campground Harbor Vista. We have stayed at all of these in a 43' 5er.

That recreation area looks great - any good suggestions for a beach spot on the way back?

We think Crater Lake is a must see/visit for an RVer. Once you peek over the rim into the lake, you won't forget it.

Some good suggestions above...
Also consider camping at these close by campgrounds:

Diamond Lake (a couple of good choices)
Joseph Stewart State Recreational Area and Campground>>>LINK

Have a good trip.

Thanks folks, this is exactly the kind of advice I needed. I'd love to go to Rainier as well, but this adds another 350 miles north from Tucson. We could certainly do all of this, but it means most of a 2 week vacation spent driving. Have to think - This might be a trip better suited to a month long northern west coast swing ...

Steve

Crater Lake is honestly a one day site seeing trip. But there are dozens of things to see and do in central Oregon. So, yea, you could easily fit a week in. Collier State Park is the closest state park to Crater Lake. But LaPine is only about an hour away and offers a lot to do.

Be aware that the snow isn't off the all roads until late June to mid July up there. The same applies to the trails. You might consider Lassen Volcanic NP. Or combining Crater Lake with Ranier.